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1356 lines
37 KiB
1356 lines
37 KiB
/* |
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* Pressure stall information for CPU, memory and IO |
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* |
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* Copyright (c) 2018 Facebook, Inc. |
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* Author: Johannes Weiner <[email protected]> |
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* |
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* Polling support by Suren Baghdasaryan <[email protected]> |
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* Copyright (c) 2018 Google, Inc. |
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* |
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* When CPU, memory and IO are contended, tasks experience delays that |
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* reduce throughput and introduce latencies into the workload. Memory |
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* and IO contention, in addition, can cause a full loss of forward |
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* progress in which the CPU goes idle. |
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* |
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* This code aggregates individual task delays into resource pressure |
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* metrics that indicate problems with both workload health and |
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* resource utilization. |
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* |
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* Model |
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* |
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* The time in which a task can execute on a CPU is our baseline for |
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* productivity. Pressure expresses the amount of time in which this |
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* potential cannot be realized due to resource contention. |
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* |
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* This concept of productivity has two components: the workload and |
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* the CPU. To measure the impact of pressure on both, we define two |
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* contention states for a resource: SOME and FULL. |
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* |
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* In the SOME state of a given resource, one or more tasks are |
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* delayed on that resource. This affects the workload's ability to |
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* perform work, but the CPU may still be executing other tasks. |
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* |
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* In the FULL state of a given resource, all non-idle tasks are |
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* delayed on that resource such that nobody is advancing and the CPU |
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* goes idle. This leaves both workload and CPU unproductive. |
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* |
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* (Naturally, the FULL state doesn't exist for the CPU resource.) |
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* |
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* SOME = nr_delayed_tasks != 0 |
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* FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0 |
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* |
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* The percentage of wallclock time spent in those compound stall |
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* states gives pressure numbers between 0 and 100 for each resource, |
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* where the SOME percentage indicates workload slowdowns and the FULL |
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* percentage indicates reduced CPU utilization: |
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* |
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* %SOME = time(SOME) / period |
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* %FULL = time(FULL) / period |
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* |
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* Multiple CPUs |
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* |
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* The more tasks and available CPUs there are, the more work can be |
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* performed concurrently. This means that the potential that can go |
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* unrealized due to resource contention *also* scales with non-idle |
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* tasks and CPUs. |
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* |
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* Consider a scenario where 257 number crunching tasks are trying to |
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* run concurrently on 256 CPUs. If we simply aggregated the task |
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* states, we would have to conclude a CPU SOME pressure number of |
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* 100%, since *somebody* is waiting on a runqueue at all |
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* times. However, that is clearly not the amount of contention the |
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* workload is experiencing: only one out of 256 possible exceution |
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* threads will be contended at any given time, or about 0.4%. |
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* |
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* Conversely, consider a scenario of 4 tasks and 4 CPUs where at any |
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* given time *one* of the tasks is delayed due to a lack of memory. |
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* Again, looking purely at the task state would yield a memory FULL |
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* pressure number of 0%, since *somebody* is always making forward |
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* progress. But again this wouldn't capture the amount of execution |
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* potential lost, which is 1 out of 4 CPUs, or 25%. |
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* |
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* To calculate wasted potential (pressure) with multiple processors, |
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* we have to base our calculation on the number of non-idle tasks in |
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* conjunction with the number of available CPUs, which is the number |
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* of potential execution threads. SOME becomes then the proportion of |
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* delayed tasks to possibe threads, and FULL is the share of possible |
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* threads that are unproductive due to delays: |
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* |
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* threads = min(nr_nonidle_tasks, nr_cpus) |
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* SOME = min(nr_delayed_tasks / threads, 1) |
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* FULL = (threads - min(nr_running_tasks, threads)) / threads |
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* |
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* For the 257 number crunchers on 256 CPUs, this yields: |
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* |
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* threads = min(257, 256) |
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* SOME = min(1 / 256, 1) = 0.4% |
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* FULL = (256 - min(257, 256)) / 256 = 0% |
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* |
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* For the 1 out of 4 memory-delayed tasks, this yields: |
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* |
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* threads = min(4, 4) |
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* SOME = min(1 / 4, 1) = 25% |
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* FULL = (4 - min(3, 4)) / 4 = 25% |
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* |
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* [ Substitute nr_cpus with 1, and you can see that it's a natural |
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* extension of the single-CPU model. ] |
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* |
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* Implementation |
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* |
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* To assess the precise time spent in each such state, we would have |
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* to freeze the system on task changes and start/stop the state |
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* clocks accordingly. Obviously that doesn't scale in practice. |
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* |
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* Because the scheduler aims to distribute the compute load evenly |
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* among the available CPUs, we can track task state locally to each |
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* CPU and, at much lower frequency, extrapolate the global state for |
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* the cumulative stall times and the running averages. |
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* |
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* For each runqueue, we track: |
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* |
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* tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) |
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* tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu]) |
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* tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) |
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* |
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* and then periodically aggregate: |
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* |
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* tNONIDLE = sum(tNONIDLE[i]) |
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* |
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* tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE |
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* tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE |
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* |
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* %SOME = tSOME / period |
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* %FULL = tFULL / period |
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* |
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* This gives us an approximation of pressure that is practical |
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* cost-wise, yet way more sensitive and accurate than periodic |
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* sampling of the aggregate task states would be. |
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*/ |
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|
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#include "../workqueue_internal.h" |
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#include <linux/sched/loadavg.h> |
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#include <linux/seq_file.h> |
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#include <linux/proc_fs.h> |
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#include <linux/seqlock.h> |
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#include <linux/uaccess.h> |
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#include <linux/cgroup.h> |
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#include <linux/module.h> |
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#include <linux/sched.h> |
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#include <linux/ctype.h> |
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#include <linux/file.h> |
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#include <linux/poll.h> |
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#include <linux/psi.h> |
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#include "sched.h" |
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|
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static int psi_bug __read_mostly; |
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|
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DEFINE_STATIC_KEY_FALSE(psi_disabled); |
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|
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#ifdef CONFIG_PSI_DEFAULT_DISABLED |
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static bool psi_enable; |
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#else |
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static bool psi_enable = true; |
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#endif |
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static int __init setup_psi(char *str) |
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{ |
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return kstrtobool(str, &psi_enable) == 0; |
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} |
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__setup("psi=", setup_psi); |
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|
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/* Running averages - we need to be higher-res than loadavg */ |
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#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ |
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#define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ |
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#define EXP_60s 1981 /* 1/exp(2s/60s) */ |
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#define EXP_300s 2034 /* 1/exp(2s/300s) */ |
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|
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/* PSI trigger definitions */ |
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#define WINDOW_MIN_US 500000 /* Min window size is 500ms */ |
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#define WINDOW_MAX_US 10000000 /* Max window size is 10s */ |
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#define UPDATES_PER_WINDOW 10 /* 10 updates per window */ |
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|
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/* Sampling frequency in nanoseconds */ |
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static u64 psi_period __read_mostly; |
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|
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/* System-level pressure and stall tracking */ |
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static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); |
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struct psi_group psi_system = { |
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.pcpu = &system_group_pcpu, |
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}; |
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|
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static void psi_avgs_work(struct work_struct *work); |
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|
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static void group_init(struct psi_group *group) |
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{ |
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int cpu; |
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|
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for_each_possible_cpu(cpu) |
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seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); |
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group->avg_last_update = sched_clock(); |
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group->avg_next_update = group->avg_last_update + psi_period; |
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INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); |
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mutex_init(&group->avgs_lock); |
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/* Init trigger-related members */ |
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mutex_init(&group->trigger_lock); |
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INIT_LIST_HEAD(&group->triggers); |
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memset(group->nr_triggers, 0, sizeof(group->nr_triggers)); |
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group->poll_states = 0; |
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group->poll_min_period = U32_MAX; |
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memset(group->polling_total, 0, sizeof(group->polling_total)); |
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group->polling_next_update = ULLONG_MAX; |
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group->polling_until = 0; |
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rcu_assign_pointer(group->poll_task, NULL); |
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} |
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void __init psi_init(void) |
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{ |
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if (!psi_enable) { |
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static_branch_enable(&psi_disabled); |
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return; |
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} |
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psi_period = jiffies_to_nsecs(PSI_FREQ); |
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group_init(&psi_system); |
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} |
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static bool test_state(unsigned int *tasks, enum psi_states state) |
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{ |
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switch (state) { |
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case PSI_IO_SOME: |
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return tasks[NR_IOWAIT]; |
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case PSI_IO_FULL: |
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return tasks[NR_IOWAIT] && !tasks[NR_RUNNING]; |
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case PSI_MEM_SOME: |
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return tasks[NR_MEMSTALL]; |
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case PSI_MEM_FULL: |
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return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]; |
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case PSI_CPU_SOME: |
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return tasks[NR_RUNNING] > tasks[NR_ONCPU]; |
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case PSI_NONIDLE: |
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return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || |
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tasks[NR_RUNNING]; |
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default: |
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return false; |
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} |
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} |
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static void get_recent_times(struct psi_group *group, int cpu, |
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enum psi_aggregators aggregator, u32 *times, |
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u32 *pchanged_states) |
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{ |
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struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); |
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u64 now, state_start; |
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enum psi_states s; |
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unsigned int seq; |
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u32 state_mask; |
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*pchanged_states = 0; |
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|
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/* Snapshot a coherent view of the CPU state */ |
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do { |
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seq = read_seqcount_begin(&groupc->seq); |
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now = cpu_clock(cpu); |
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memcpy(times, groupc->times, sizeof(groupc->times)); |
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state_mask = groupc->state_mask; |
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state_start = groupc->state_start; |
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} while (read_seqcount_retry(&groupc->seq, seq)); |
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|
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/* Calculate state time deltas against the previous snapshot */ |
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for (s = 0; s < NR_PSI_STATES; s++) { |
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u32 delta; |
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/* |
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* In addition to already concluded states, we also |
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* incorporate currently active states on the CPU, |
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* since states may last for many sampling periods. |
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* |
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* This way we keep our delta sampling buckets small |
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* (u32) and our reported pressure close to what's |
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* actually happening. |
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*/ |
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if (state_mask & (1 << s)) |
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times[s] += now - state_start; |
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delta = times[s] - groupc->times_prev[aggregator][s]; |
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groupc->times_prev[aggregator][s] = times[s]; |
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times[s] = delta; |
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if (delta) |
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*pchanged_states |= (1 << s); |
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} |
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} |
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static void calc_avgs(unsigned long avg[3], int missed_periods, |
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u64 time, u64 period) |
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{ |
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unsigned long pct; |
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|
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/* Fill in zeroes for periods of no activity */ |
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if (missed_periods) { |
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avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); |
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avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); |
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avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); |
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} |
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/* Sample the most recent active period */ |
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pct = div_u64(time * 100, period); |
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pct *= FIXED_1; |
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avg[0] = calc_load(avg[0], EXP_10s, pct); |
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avg[1] = calc_load(avg[1], EXP_60s, pct); |
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avg[2] = calc_load(avg[2], EXP_300s, pct); |
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} |
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static void collect_percpu_times(struct psi_group *group, |
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enum psi_aggregators aggregator, |
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u32 *pchanged_states) |
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{ |
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u64 deltas[NR_PSI_STATES - 1] = { 0, }; |
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unsigned long nonidle_total = 0; |
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u32 changed_states = 0; |
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int cpu; |
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int s; |
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|
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/* |
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* Collect the per-cpu time buckets and average them into a |
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* single time sample that is normalized to wallclock time. |
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* |
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* For averaging, each CPU is weighted by its non-idle time in |
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* the sampling period. This eliminates artifacts from uneven |
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* loading, or even entirely idle CPUs. |
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*/ |
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for_each_possible_cpu(cpu) { |
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u32 times[NR_PSI_STATES]; |
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u32 nonidle; |
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u32 cpu_changed_states; |
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get_recent_times(group, cpu, aggregator, times, |
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&cpu_changed_states); |
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changed_states |= cpu_changed_states; |
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nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); |
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nonidle_total += nonidle; |
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for (s = 0; s < PSI_NONIDLE; s++) |
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deltas[s] += (u64)times[s] * nonidle; |
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} |
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|
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/* |
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* Integrate the sample into the running statistics that are |
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* reported to userspace: the cumulative stall times and the |
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* decaying averages. |
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* |
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* Pressure percentages are sampled at PSI_FREQ. We might be |
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* called more often when the user polls more frequently than |
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* that; we might be called less often when there is no task |
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* activity, thus no data, and clock ticks are sporadic. The |
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* below handles both. |
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*/ |
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|
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/* total= */ |
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for (s = 0; s < NR_PSI_STATES - 1; s++) |
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group->total[aggregator][s] += |
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div_u64(deltas[s], max(nonidle_total, 1UL)); |
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if (pchanged_states) |
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*pchanged_states = changed_states; |
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} |
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static u64 update_averages(struct psi_group *group, u64 now) |
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{ |
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unsigned long missed_periods = 0; |
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u64 expires, period; |
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u64 avg_next_update; |
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int s; |
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|
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/* avgX= */ |
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expires = group->avg_next_update; |
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if (now - expires >= psi_period) |
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missed_periods = div_u64(now - expires, psi_period); |
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|
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/* |
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* The periodic clock tick can get delayed for various |
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* reasons, especially on loaded systems. To avoid clock |
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* drift, we schedule the clock in fixed psi_period intervals. |
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* But the deltas we sample out of the per-cpu buckets above |
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* are based on the actual time elapsing between clock ticks. |
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*/ |
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avg_next_update = expires + ((1 + missed_periods) * psi_period); |
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period = now - (group->avg_last_update + (missed_periods * psi_period)); |
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group->avg_last_update = now; |
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|
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for (s = 0; s < NR_PSI_STATES - 1; s++) { |
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u32 sample; |
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|
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sample = group->total[PSI_AVGS][s] - group->avg_total[s]; |
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/* |
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* Due to the lockless sampling of the time buckets, |
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* recorded time deltas can slip into the next period, |
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* which under full pressure can result in samples in |
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* excess of the period length. |
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* |
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* We don't want to report non-sensical pressures in |
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* excess of 100%, nor do we want to drop such events |
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* on the floor. Instead we punt any overage into the |
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* future until pressure subsides. By doing this we |
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* don't underreport the occurring pressure curve, we |
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* just report it delayed by one period length. |
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* |
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* The error isn't cumulative. As soon as another |
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* delta slips from a period P to P+1, by definition |
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* it frees up its time T in P. |
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*/ |
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if (sample > period) |
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sample = period; |
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group->avg_total[s] += sample; |
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calc_avgs(group->avg[s], missed_periods, sample, period); |
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} |
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|
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return avg_next_update; |
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} |
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|
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static void psi_avgs_work(struct work_struct *work) |
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{ |
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struct delayed_work *dwork; |
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struct psi_group *group; |
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u32 changed_states; |
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bool nonidle; |
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u64 now; |
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|
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dwork = to_delayed_work(work); |
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group = container_of(dwork, struct psi_group, avgs_work); |
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|
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mutex_lock(&group->avgs_lock); |
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|
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now = sched_clock(); |
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|
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collect_percpu_times(group, PSI_AVGS, &changed_states); |
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nonidle = changed_states & (1 << PSI_NONIDLE); |
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/* |
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* If there is task activity, periodically fold the per-cpu |
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* times and feed samples into the running averages. If things |
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* are idle and there is no data to process, stop the clock. |
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* Once restarted, we'll catch up the running averages in one |
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* go - see calc_avgs() and missed_periods. |
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*/ |
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if (now >= group->avg_next_update) |
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group->avg_next_update = update_averages(group, now); |
|
|
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if (nonidle) { |
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schedule_delayed_work(dwork, nsecs_to_jiffies( |
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group->avg_next_update - now) + 1); |
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} |
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|
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mutex_unlock(&group->avgs_lock); |
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} |
|
|
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/* Trigger tracking window manupulations */ |
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static void window_reset(struct psi_window *win, u64 now, u64 value, |
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u64 prev_growth) |
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{ |
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win->start_time = now; |
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win->start_value = value; |
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win->prev_growth = prev_growth; |
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} |
|
|
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/* |
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* PSI growth tracking window update and growth calculation routine. |
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* |
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* This approximates a sliding tracking window by interpolating |
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* partially elapsed windows using historical growth data from the |
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* previous intervals. This minimizes memory requirements (by not storing |
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* all the intermediate values in the previous window) and simplifies |
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* the calculations. It works well because PSI signal changes only in |
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* positive direction and over relatively small window sizes the growth |
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* is close to linear. |
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*/ |
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static u64 window_update(struct psi_window *win, u64 now, u64 value) |
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{ |
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u64 elapsed; |
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u64 growth; |
|
|
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elapsed = now - win->start_time; |
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growth = value - win->start_value; |
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/* |
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* After each tracking window passes win->start_value and |
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* win->start_time get reset and win->prev_growth stores |
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* the average per-window growth of the previous window. |
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* win->prev_growth is then used to interpolate additional |
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* growth from the previous window assuming it was linear. |
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*/ |
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if (elapsed > win->size) |
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window_reset(win, now, value, growth); |
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else { |
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u32 remaining; |
|
|
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remaining = win->size - elapsed; |
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growth += div64_u64(win->prev_growth * remaining, win->size); |
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} |
|
|
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return growth; |
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} |
|
|
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static void init_triggers(struct psi_group *group, u64 now) |
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{ |
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struct psi_trigger *t; |
|
|
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list_for_each_entry(t, &group->triggers, node) |
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window_reset(&t->win, now, |
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group->total[PSI_POLL][t->state], 0); |
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memcpy(group->polling_total, group->total[PSI_POLL], |
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sizeof(group->polling_total)); |
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group->polling_next_update = now + group->poll_min_period; |
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} |
|
|
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static u64 update_triggers(struct psi_group *group, u64 now) |
|
{ |
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struct psi_trigger *t; |
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bool new_stall = false; |
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u64 *total = group->total[PSI_POLL]; |
|
|
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/* |
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* On subsequent updates, calculate growth deltas and let |
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* watchers know when their specified thresholds are exceeded. |
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*/ |
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list_for_each_entry(t, &group->triggers, node) { |
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u64 growth; |
|
|
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/* Check for stall activity */ |
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if (group->polling_total[t->state] == total[t->state]) |
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continue; |
|
|
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/* |
|
* Multiple triggers might be looking at the same state, |
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* remember to update group->polling_total[] once we've |
|
* been through all of them. Also remember to extend the |
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* polling time if we see new stall activity. |
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*/ |
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new_stall = true; |
|
|
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/* Calculate growth since last update */ |
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growth = window_update(&t->win, now, total[t->state]); |
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if (growth < t->threshold) |
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continue; |
|
|
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/* Limit event signaling to once per window */ |
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if (now < t->last_event_time + t->win.size) |
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continue; |
|
|
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/* Generate an event */ |
|
if (cmpxchg(&t->event, 0, 1) == 0) |
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wake_up_interruptible(&t->event_wait); |
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t->last_event_time = now; |
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} |
|
|
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if (new_stall) |
|
memcpy(group->polling_total, total, |
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sizeof(group->polling_total)); |
|
|
|
return now + group->poll_min_period; |
|
} |
|
|
|
/* Schedule polling if it's not already scheduled. */ |
|
static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay) |
|
{ |
|
struct task_struct *task; |
|
|
|
/* |
|
* Do not reschedule if already scheduled. |
|
* Possible race with a timer scheduled after this check but before |
|
* mod_timer below can be tolerated because group->polling_next_update |
|
* will keep updates on schedule. |
|
*/ |
|
if (timer_pending(&group->poll_timer)) |
|
return; |
|
|
|
rcu_read_lock(); |
|
|
|
task = rcu_dereference(group->poll_task); |
|
/* |
|
* kworker might be NULL in case psi_trigger_destroy races with |
|
* psi_task_change (hotpath) which can't use locks |
|
*/ |
|
if (likely(task)) |
|
mod_timer(&group->poll_timer, jiffies + delay); |
|
|
|
rcu_read_unlock(); |
|
} |
|
|
|
static void psi_poll_work(struct psi_group *group) |
|
{ |
|
u32 changed_states; |
|
u64 now; |
|
|
|
mutex_lock(&group->trigger_lock); |
|
|
|
now = sched_clock(); |
|
|
|
collect_percpu_times(group, PSI_POLL, &changed_states); |
|
|
|
if (changed_states & group->poll_states) { |
|
/* Initialize trigger windows when entering polling mode */ |
|
if (now > group->polling_until) |
|
init_triggers(group, now); |
|
|
|
/* |
|
* Keep the monitor active for at least the duration of the |
|
* minimum tracking window as long as monitor states are |
|
* changing. |
|
*/ |
|
group->polling_until = now + |
|
group->poll_min_period * UPDATES_PER_WINDOW; |
|
} |
|
|
|
if (now > group->polling_until) { |
|
group->polling_next_update = ULLONG_MAX; |
|
goto out; |
|
} |
|
|
|
if (now >= group->polling_next_update) |
|
group->polling_next_update = update_triggers(group, now); |
|
|
|
psi_schedule_poll_work(group, |
|
nsecs_to_jiffies(group->polling_next_update - now) + 1); |
|
|
|
out: |
|
mutex_unlock(&group->trigger_lock); |
|
} |
|
|
|
static int psi_poll_worker(void *data) |
|
{ |
|
struct psi_group *group = (struct psi_group *)data; |
|
|
|
sched_set_fifo_low(current); |
|
|
|
while (true) { |
|
wait_event_interruptible(group->poll_wait, |
|
atomic_cmpxchg(&group->poll_wakeup, 1, 0) || |
|
kthread_should_stop()); |
|
if (kthread_should_stop()) |
|
break; |
|
|
|
psi_poll_work(group); |
|
} |
|
return 0; |
|
} |
|
|
|
static void poll_timer_fn(struct timer_list *t) |
|
{ |
|
struct psi_group *group = from_timer(group, t, poll_timer); |
|
|
|
atomic_set(&group->poll_wakeup, 1); |
|
wake_up_interruptible(&group->poll_wait); |
|
} |
|
|
|
static void record_times(struct psi_group_cpu *groupc, int cpu, |
|
bool memstall_tick) |
|
{ |
|
u32 delta; |
|
u64 now; |
|
|
|
now = cpu_clock(cpu); |
|
delta = now - groupc->state_start; |
|
groupc->state_start = now; |
|
|
|
if (groupc->state_mask & (1 << PSI_IO_SOME)) { |
|
groupc->times[PSI_IO_SOME] += delta; |
|
if (groupc->state_mask & (1 << PSI_IO_FULL)) |
|
groupc->times[PSI_IO_FULL] += delta; |
|
} |
|
|
|
if (groupc->state_mask & (1 << PSI_MEM_SOME)) { |
|
groupc->times[PSI_MEM_SOME] += delta; |
|
if (groupc->state_mask & (1 << PSI_MEM_FULL)) |
|
groupc->times[PSI_MEM_FULL] += delta; |
|
else if (memstall_tick) { |
|
u32 sample; |
|
/* |
|
* Since we care about lost potential, a |
|
* memstall is FULL when there are no other |
|
* working tasks, but also when the CPU is |
|
* actively reclaiming and nothing productive |
|
* could run even if it were runnable. |
|
* |
|
* When the timer tick sees a reclaiming CPU, |
|
* regardless of runnable tasks, sample a FULL |
|
* tick (or less if it hasn't been a full tick |
|
* since the last state change). |
|
*/ |
|
sample = min(delta, (u32)jiffies_to_nsecs(1)); |
|
groupc->times[PSI_MEM_FULL] += sample; |
|
} |
|
} |
|
|
|
if (groupc->state_mask & (1 << PSI_CPU_SOME)) |
|
groupc->times[PSI_CPU_SOME] += delta; |
|
|
|
if (groupc->state_mask & (1 << PSI_NONIDLE)) |
|
groupc->times[PSI_NONIDLE] += delta; |
|
} |
|
|
|
static void psi_group_change(struct psi_group *group, int cpu, |
|
unsigned int clear, unsigned int set, |
|
bool wake_clock) |
|
{ |
|
struct psi_group_cpu *groupc; |
|
u32 state_mask = 0; |
|
unsigned int t, m; |
|
enum psi_states s; |
|
|
|
groupc = per_cpu_ptr(group->pcpu, cpu); |
|
|
|
/* |
|
* First we assess the aggregate resource states this CPU's |
|
* tasks have been in since the last change, and account any |
|
* SOME and FULL time these may have resulted in. |
|
* |
|
* Then we update the task counts according to the state |
|
* change requested through the @clear and @set bits. |
|
*/ |
|
write_seqcount_begin(&groupc->seq); |
|
|
|
record_times(groupc, cpu, false); |
|
|
|
for (t = 0, m = clear; m; m &= ~(1 << t), t++) { |
|
if (!(m & (1 << t))) |
|
continue; |
|
if (groupc->tasks[t]) { |
|
groupc->tasks[t]--; |
|
} else if (!psi_bug) { |
|
printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", |
|
cpu, t, groupc->tasks[0], |
|
groupc->tasks[1], groupc->tasks[2], |
|
groupc->tasks[3], clear, set); |
|
psi_bug = 1; |
|
} |
|
} |
|
|
|
for (t = 0; set; set &= ~(1 << t), t++) |
|
if (set & (1 << t)) |
|
groupc->tasks[t]++; |
|
|
|
/* Calculate state mask representing active states */ |
|
for (s = 0; s < NR_PSI_STATES; s++) { |
|
if (test_state(groupc->tasks, s)) |
|
state_mask |= (1 << s); |
|
} |
|
groupc->state_mask = state_mask; |
|
|
|
write_seqcount_end(&groupc->seq); |
|
|
|
if (state_mask & group->poll_states) |
|
psi_schedule_poll_work(group, 1); |
|
|
|
if (wake_clock && !delayed_work_pending(&group->avgs_work)) |
|
schedule_delayed_work(&group->avgs_work, PSI_FREQ); |
|
} |
|
|
|
static struct psi_group *iterate_groups(struct task_struct *task, void **iter) |
|
{ |
|
#ifdef CONFIG_CGROUPS |
|
struct cgroup *cgroup = NULL; |
|
|
|
if (!*iter) |
|
cgroup = task->cgroups->dfl_cgrp; |
|
else if (*iter == &psi_system) |
|
return NULL; |
|
else |
|
cgroup = cgroup_parent(*iter); |
|
|
|
if (cgroup && cgroup_parent(cgroup)) { |
|
*iter = cgroup; |
|
return cgroup_psi(cgroup); |
|
} |
|
#else |
|
if (*iter) |
|
return NULL; |
|
#endif |
|
*iter = &psi_system; |
|
return &psi_system; |
|
} |
|
|
|
static void psi_flags_change(struct task_struct *task, int clear, int set) |
|
{ |
|
if (((task->psi_flags & set) || |
|
(task->psi_flags & clear) != clear) && |
|
!psi_bug) { |
|
printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", |
|
task->pid, task->comm, task_cpu(task), |
|
task->psi_flags, clear, set); |
|
psi_bug = 1; |
|
} |
|
|
|
task->psi_flags &= ~clear; |
|
task->psi_flags |= set; |
|
} |
|
|
|
void psi_task_change(struct task_struct *task, int clear, int set) |
|
{ |
|
int cpu = task_cpu(task); |
|
struct psi_group *group; |
|
bool wake_clock = true; |
|
void *iter = NULL; |
|
|
|
if (!task->pid) |
|
return; |
|
|
|
psi_flags_change(task, clear, set); |
|
|
|
/* |
|
* Periodic aggregation shuts off if there is a period of no |
|
* task changes, so we wake it back up if necessary. However, |
|
* don't do this if the task change is the aggregation worker |
|
* itself going to sleep, or we'll ping-pong forever. |
|
*/ |
|
if (unlikely((clear & TSK_RUNNING) && |
|
(task->flags & PF_WQ_WORKER) && |
|
wq_worker_last_func(task) == psi_avgs_work)) |
|
wake_clock = false; |
|
|
|
while ((group = iterate_groups(task, &iter))) |
|
psi_group_change(group, cpu, clear, set, wake_clock); |
|
} |
|
|
|
void psi_task_switch(struct task_struct *prev, struct task_struct *next, |
|
bool sleep) |
|
{ |
|
struct psi_group *group, *common = NULL; |
|
int cpu = task_cpu(prev); |
|
void *iter; |
|
|
|
if (next->pid) { |
|
psi_flags_change(next, 0, TSK_ONCPU); |
|
/* |
|
* When moving state between tasks, the group that |
|
* contains them both does not change: we can stop |
|
* updating the tree once we reach the first common |
|
* ancestor. Iterate @next's ancestors until we |
|
* encounter @prev's state. |
|
*/ |
|
iter = NULL; |
|
while ((group = iterate_groups(next, &iter))) { |
|
if (per_cpu_ptr(group->pcpu, cpu)->tasks[NR_ONCPU]) { |
|
common = group; |
|
break; |
|
} |
|
|
|
psi_group_change(group, cpu, 0, TSK_ONCPU, true); |
|
} |
|
} |
|
|
|
/* |
|
* If this is a voluntary sleep, dequeue will have taken care |
|
* of the outgoing TSK_ONCPU alongside TSK_RUNNING already. We |
|
* only need to deal with it during preemption. |
|
*/ |
|
if (sleep) |
|
return; |
|
|
|
if (prev->pid) { |
|
psi_flags_change(prev, TSK_ONCPU, 0); |
|
|
|
iter = NULL; |
|
while ((group = iterate_groups(prev, &iter)) && group != common) |
|
psi_group_change(group, cpu, TSK_ONCPU, 0, true); |
|
} |
|
} |
|
|
|
void psi_memstall_tick(struct task_struct *task, int cpu) |
|
{ |
|
struct psi_group *group; |
|
void *iter = NULL; |
|
|
|
while ((group = iterate_groups(task, &iter))) { |
|
struct psi_group_cpu *groupc; |
|
|
|
groupc = per_cpu_ptr(group->pcpu, cpu); |
|
write_seqcount_begin(&groupc->seq); |
|
record_times(groupc, cpu, true); |
|
write_seqcount_end(&groupc->seq); |
|
} |
|
} |
|
|
|
/** |
|
* psi_memstall_enter - mark the beginning of a memory stall section |
|
* @flags: flags to handle nested sections |
|
* |
|
* Marks the calling task as being stalled due to a lack of memory, |
|
* such as waiting for a refault or performing reclaim. |
|
*/ |
|
void psi_memstall_enter(unsigned long *flags) |
|
{ |
|
struct rq_flags rf; |
|
struct rq *rq; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return; |
|
|
|
*flags = current->in_memstall; |
|
if (*flags) |
|
return; |
|
/* |
|
* in_memstall setting & accounting needs to be atomic wrt |
|
* changes to the task's scheduling state, otherwise we can |
|
* race with CPU migration. |
|
*/ |
|
rq = this_rq_lock_irq(&rf); |
|
|
|
current->in_memstall = 1; |
|
psi_task_change(current, 0, TSK_MEMSTALL); |
|
|
|
rq_unlock_irq(rq, &rf); |
|
} |
|
|
|
/** |
|
* psi_memstall_leave - mark the end of an memory stall section |
|
* @flags: flags to handle nested memdelay sections |
|
* |
|
* Marks the calling task as no longer stalled due to lack of memory. |
|
*/ |
|
void psi_memstall_leave(unsigned long *flags) |
|
{ |
|
struct rq_flags rf; |
|
struct rq *rq; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return; |
|
|
|
if (*flags) |
|
return; |
|
/* |
|
* in_memstall clearing & accounting needs to be atomic wrt |
|
* changes to the task's scheduling state, otherwise we could |
|
* race with CPU migration. |
|
*/ |
|
rq = this_rq_lock_irq(&rf); |
|
|
|
current->in_memstall = 0; |
|
psi_task_change(current, TSK_MEMSTALL, 0); |
|
|
|
rq_unlock_irq(rq, &rf); |
|
} |
|
|
|
#ifdef CONFIG_CGROUPS |
|
int psi_cgroup_alloc(struct cgroup *cgroup) |
|
{ |
|
if (static_branch_likely(&psi_disabled)) |
|
return 0; |
|
|
|
cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu); |
|
if (!cgroup->psi.pcpu) |
|
return -ENOMEM; |
|
group_init(&cgroup->psi); |
|
return 0; |
|
} |
|
|
|
void psi_cgroup_free(struct cgroup *cgroup) |
|
{ |
|
if (static_branch_likely(&psi_disabled)) |
|
return; |
|
|
|
cancel_delayed_work_sync(&cgroup->psi.avgs_work); |
|
free_percpu(cgroup->psi.pcpu); |
|
/* All triggers must be removed by now */ |
|
WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n"); |
|
} |
|
|
|
/** |
|
* cgroup_move_task - move task to a different cgroup |
|
* @task: the task |
|
* @to: the target css_set |
|
* |
|
* Move task to a new cgroup and safely migrate its associated stall |
|
* state between the different groups. |
|
* |
|
* This function acquires the task's rq lock to lock out concurrent |
|
* changes to the task's scheduling state and - in case the task is |
|
* running - concurrent changes to its stall state. |
|
*/ |
|
void cgroup_move_task(struct task_struct *task, struct css_set *to) |
|
{ |
|
unsigned int task_flags = 0; |
|
struct rq_flags rf; |
|
struct rq *rq; |
|
|
|
if (static_branch_likely(&psi_disabled)) { |
|
/* |
|
* Lame to do this here, but the scheduler cannot be locked |
|
* from the outside, so we move cgroups from inside sched/. |
|
*/ |
|
rcu_assign_pointer(task->cgroups, to); |
|
return; |
|
} |
|
|
|
rq = task_rq_lock(task, &rf); |
|
|
|
if (task_on_rq_queued(task)) { |
|
task_flags = TSK_RUNNING; |
|
if (task_current(rq, task)) |
|
task_flags |= TSK_ONCPU; |
|
} else if (task->in_iowait) |
|
task_flags = TSK_IOWAIT; |
|
|
|
if (task->in_memstall) |
|
task_flags |= TSK_MEMSTALL; |
|
|
|
if (task_flags) |
|
psi_task_change(task, task_flags, 0); |
|
|
|
/* See comment above */ |
|
rcu_assign_pointer(task->cgroups, to); |
|
|
|
if (task_flags) |
|
psi_task_change(task, 0, task_flags); |
|
|
|
task_rq_unlock(rq, task, &rf); |
|
} |
|
#endif /* CONFIG_CGROUPS */ |
|
|
|
int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) |
|
{ |
|
int full; |
|
u64 now; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return -EOPNOTSUPP; |
|
|
|
/* Update averages before reporting them */ |
|
mutex_lock(&group->avgs_lock); |
|
now = sched_clock(); |
|
collect_percpu_times(group, PSI_AVGS, NULL); |
|
if (now >= group->avg_next_update) |
|
group->avg_next_update = update_averages(group, now); |
|
mutex_unlock(&group->avgs_lock); |
|
|
|
for (full = 0; full < 2 - (res == PSI_CPU); full++) { |
|
unsigned long avg[3]; |
|
u64 total; |
|
int w; |
|
|
|
for (w = 0; w < 3; w++) |
|
avg[w] = group->avg[res * 2 + full][w]; |
|
total = div_u64(group->total[PSI_AVGS][res * 2 + full], |
|
NSEC_PER_USEC); |
|
|
|
seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", |
|
full ? "full" : "some", |
|
LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), |
|
LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), |
|
LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), |
|
total); |
|
} |
|
|
|
return 0; |
|
} |
|
|
|
static int psi_io_show(struct seq_file *m, void *v) |
|
{ |
|
return psi_show(m, &psi_system, PSI_IO); |
|
} |
|
|
|
static int psi_memory_show(struct seq_file *m, void *v) |
|
{ |
|
return psi_show(m, &psi_system, PSI_MEM); |
|
} |
|
|
|
static int psi_cpu_show(struct seq_file *m, void *v) |
|
{ |
|
return psi_show(m, &psi_system, PSI_CPU); |
|
} |
|
|
|
static int psi_io_open(struct inode *inode, struct file *file) |
|
{ |
|
return single_open(file, psi_io_show, NULL); |
|
} |
|
|
|
static int psi_memory_open(struct inode *inode, struct file *file) |
|
{ |
|
return single_open(file, psi_memory_show, NULL); |
|
} |
|
|
|
static int psi_cpu_open(struct inode *inode, struct file *file) |
|
{ |
|
return single_open(file, psi_cpu_show, NULL); |
|
} |
|
|
|
struct psi_trigger *psi_trigger_create(struct psi_group *group, |
|
char *buf, size_t nbytes, enum psi_res res) |
|
{ |
|
struct psi_trigger *t; |
|
enum psi_states state; |
|
u32 threshold_us; |
|
u32 window_us; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return ERR_PTR(-EOPNOTSUPP); |
|
|
|
if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) |
|
state = PSI_IO_SOME + res * 2; |
|
else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) |
|
state = PSI_IO_FULL + res * 2; |
|
else |
|
return ERR_PTR(-EINVAL); |
|
|
|
if (state >= PSI_NONIDLE) |
|
return ERR_PTR(-EINVAL); |
|
|
|
if (window_us < WINDOW_MIN_US || |
|
window_us > WINDOW_MAX_US) |
|
return ERR_PTR(-EINVAL); |
|
|
|
/* Check threshold */ |
|
if (threshold_us == 0 || threshold_us > window_us) |
|
return ERR_PTR(-EINVAL); |
|
|
|
t = kmalloc(sizeof(*t), GFP_KERNEL); |
|
if (!t) |
|
return ERR_PTR(-ENOMEM); |
|
|
|
t->group = group; |
|
t->state = state; |
|
t->threshold = threshold_us * NSEC_PER_USEC; |
|
t->win.size = window_us * NSEC_PER_USEC; |
|
window_reset(&t->win, 0, 0, 0); |
|
|
|
t->event = 0; |
|
t->last_event_time = 0; |
|
init_waitqueue_head(&t->event_wait); |
|
kref_init(&t->refcount); |
|
|
|
mutex_lock(&group->trigger_lock); |
|
|
|
if (!rcu_access_pointer(group->poll_task)) { |
|
struct task_struct *task; |
|
|
|
task = kthread_create(psi_poll_worker, group, "psimon"); |
|
if (IS_ERR(task)) { |
|
kfree(t); |
|
mutex_unlock(&group->trigger_lock); |
|
return ERR_CAST(task); |
|
} |
|
atomic_set(&group->poll_wakeup, 0); |
|
init_waitqueue_head(&group->poll_wait); |
|
wake_up_process(task); |
|
timer_setup(&group->poll_timer, poll_timer_fn, 0); |
|
rcu_assign_pointer(group->poll_task, task); |
|
} |
|
|
|
list_add(&t->node, &group->triggers); |
|
group->poll_min_period = min(group->poll_min_period, |
|
div_u64(t->win.size, UPDATES_PER_WINDOW)); |
|
group->nr_triggers[t->state]++; |
|
group->poll_states |= (1 << t->state); |
|
|
|
mutex_unlock(&group->trigger_lock); |
|
|
|
return t; |
|
} |
|
|
|
static void psi_trigger_destroy(struct kref *ref) |
|
{ |
|
struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount); |
|
struct psi_group *group = t->group; |
|
struct task_struct *task_to_destroy = NULL; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return; |
|
|
|
/* |
|
* Wakeup waiters to stop polling. Can happen if cgroup is deleted |
|
* from under a polling process. |
|
*/ |
|
wake_up_interruptible(&t->event_wait); |
|
|
|
mutex_lock(&group->trigger_lock); |
|
|
|
if (!list_empty(&t->node)) { |
|
struct psi_trigger *tmp; |
|
u64 period = ULLONG_MAX; |
|
|
|
list_del(&t->node); |
|
group->nr_triggers[t->state]--; |
|
if (!group->nr_triggers[t->state]) |
|
group->poll_states &= ~(1 << t->state); |
|
/* reset min update period for the remaining triggers */ |
|
list_for_each_entry(tmp, &group->triggers, node) |
|
period = min(period, div_u64(tmp->win.size, |
|
UPDATES_PER_WINDOW)); |
|
group->poll_min_period = period; |
|
/* Destroy poll_task when the last trigger is destroyed */ |
|
if (group->poll_states == 0) { |
|
group->polling_until = 0; |
|
task_to_destroy = rcu_dereference_protected( |
|
group->poll_task, |
|
lockdep_is_held(&group->trigger_lock)); |
|
rcu_assign_pointer(group->poll_task, NULL); |
|
} |
|
} |
|
|
|
mutex_unlock(&group->trigger_lock); |
|
|
|
/* |
|
* Wait for both *trigger_ptr from psi_trigger_replace and |
|
* poll_task RCUs to complete their read-side critical sections |
|
* before destroying the trigger and optionally the poll_task |
|
*/ |
|
synchronize_rcu(); |
|
/* |
|
* Destroy the kworker after releasing trigger_lock to prevent a |
|
* deadlock while waiting for psi_poll_work to acquire trigger_lock |
|
*/ |
|
if (task_to_destroy) { |
|
/* |
|
* After the RCU grace period has expired, the worker |
|
* can no longer be found through group->poll_task. |
|
* But it might have been already scheduled before |
|
* that - deschedule it cleanly before destroying it. |
|
*/ |
|
del_timer_sync(&group->poll_timer); |
|
kthread_stop(task_to_destroy); |
|
} |
|
kfree(t); |
|
} |
|
|
|
void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new) |
|
{ |
|
struct psi_trigger *old = *trigger_ptr; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return; |
|
|
|
rcu_assign_pointer(*trigger_ptr, new); |
|
if (old) |
|
kref_put(&old->refcount, psi_trigger_destroy); |
|
} |
|
|
|
__poll_t psi_trigger_poll(void **trigger_ptr, |
|
struct file *file, poll_table *wait) |
|
{ |
|
__poll_t ret = DEFAULT_POLLMASK; |
|
struct psi_trigger *t; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; |
|
|
|
rcu_read_lock(); |
|
|
|
t = rcu_dereference(*(void __rcu __force **)trigger_ptr); |
|
if (!t) { |
|
rcu_read_unlock(); |
|
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; |
|
} |
|
kref_get(&t->refcount); |
|
|
|
rcu_read_unlock(); |
|
|
|
poll_wait(file, &t->event_wait, wait); |
|
|
|
if (cmpxchg(&t->event, 1, 0) == 1) |
|
ret |= EPOLLPRI; |
|
|
|
kref_put(&t->refcount, psi_trigger_destroy); |
|
|
|
return ret; |
|
} |
|
|
|
static ssize_t psi_write(struct file *file, const char __user *user_buf, |
|
size_t nbytes, enum psi_res res) |
|
{ |
|
char buf[32]; |
|
size_t buf_size; |
|
struct seq_file *seq; |
|
struct psi_trigger *new; |
|
|
|
if (static_branch_likely(&psi_disabled)) |
|
return -EOPNOTSUPP; |
|
|
|
if (!nbytes) |
|
return -EINVAL; |
|
|
|
buf_size = min(nbytes, sizeof(buf)); |
|
if (copy_from_user(buf, user_buf, buf_size)) |
|
return -EFAULT; |
|
|
|
buf[buf_size - 1] = '\0'; |
|
|
|
new = psi_trigger_create(&psi_system, buf, nbytes, res); |
|
if (IS_ERR(new)) |
|
return PTR_ERR(new); |
|
|
|
seq = file->private_data; |
|
/* Take seq->lock to protect seq->private from concurrent writes */ |
|
mutex_lock(&seq->lock); |
|
psi_trigger_replace(&seq->private, new); |
|
mutex_unlock(&seq->lock); |
|
|
|
return nbytes; |
|
} |
|
|
|
static ssize_t psi_io_write(struct file *file, const char __user *user_buf, |
|
size_t nbytes, loff_t *ppos) |
|
{ |
|
return psi_write(file, user_buf, nbytes, PSI_IO); |
|
} |
|
|
|
static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, |
|
size_t nbytes, loff_t *ppos) |
|
{ |
|
return psi_write(file, user_buf, nbytes, PSI_MEM); |
|
} |
|
|
|
static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, |
|
size_t nbytes, loff_t *ppos) |
|
{ |
|
return psi_write(file, user_buf, nbytes, PSI_CPU); |
|
} |
|
|
|
static __poll_t psi_fop_poll(struct file *file, poll_table *wait) |
|
{ |
|
struct seq_file *seq = file->private_data; |
|
|
|
return psi_trigger_poll(&seq->private, file, wait); |
|
} |
|
|
|
static int psi_fop_release(struct inode *inode, struct file *file) |
|
{ |
|
struct seq_file *seq = file->private_data; |
|
|
|
psi_trigger_replace(&seq->private, NULL); |
|
return single_release(inode, file); |
|
} |
|
|
|
static const struct proc_ops psi_io_proc_ops = { |
|
.proc_open = psi_io_open, |
|
.proc_read = seq_read, |
|
.proc_lseek = seq_lseek, |
|
.proc_write = psi_io_write, |
|
.proc_poll = psi_fop_poll, |
|
.proc_release = psi_fop_release, |
|
}; |
|
|
|
static const struct proc_ops psi_memory_proc_ops = { |
|
.proc_open = psi_memory_open, |
|
.proc_read = seq_read, |
|
.proc_lseek = seq_lseek, |
|
.proc_write = psi_memory_write, |
|
.proc_poll = psi_fop_poll, |
|
.proc_release = psi_fop_release, |
|
}; |
|
|
|
static const struct proc_ops psi_cpu_proc_ops = { |
|
.proc_open = psi_cpu_open, |
|
.proc_read = seq_read, |
|
.proc_lseek = seq_lseek, |
|
.proc_write = psi_cpu_write, |
|
.proc_poll = psi_fop_poll, |
|
.proc_release = psi_fop_release, |
|
}; |
|
|
|
static int __init psi_proc_init(void) |
|
{ |
|
if (psi_enable) { |
|
proc_mkdir("pressure", NULL); |
|
proc_create("pressure/io", 0, NULL, &psi_io_proc_ops); |
|
proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops); |
|
proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops); |
|
} |
|
return 0; |
|
} |
|
module_init(psi_proc_init);
|
|
|