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283 lines
7.2 KiB
283 lines
7.2 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* latencytop.c: Latency display infrastructure |
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* |
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* (C) Copyright 2008 Intel Corporation |
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* Author: Arjan van de Ven <[email protected]> |
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*/ |
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/* |
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* CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is |
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* used by the "latencytop" userspace tool. The latency that is tracked is not |
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* the 'traditional' interrupt latency (which is primarily caused by something |
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* else consuming CPU), but instead, it is the latency an application encounters |
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* because the kernel sleeps on its behalf for various reasons. |
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* |
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* This code tracks 2 levels of statistics: |
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* 1) System level latency |
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* 2) Per process latency |
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* |
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* The latency is stored in fixed sized data structures in an accumulated form; |
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* if the "same" latency cause is hit twice, this will be tracked as one entry |
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* in the data structure. Both the count, total accumulated latency and maximum |
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* latency are tracked in this data structure. When the fixed size structure is |
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* full, no new causes are tracked until the buffer is flushed by writing to |
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* the /proc file; the userspace tool does this on a regular basis. |
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* |
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* A latency cause is identified by a stringified backtrace at the point that |
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* the scheduler gets invoked. The userland tool will use this string to |
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* identify the cause of the latency in human readable form. |
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* |
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* The information is exported via /proc/latency_stats and /proc/<pid>/latency. |
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* These files look like this: |
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* |
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* Latency Top version : v0.1 |
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* 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl |
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* | | | | |
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* | | | +----> the stringified backtrace |
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* | | +---------> The maximum latency for this entry in microseconds |
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* | +--------------> The accumulated latency for this entry (microseconds) |
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* +-------------------> The number of times this entry is hit |
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* |
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* (note: the average latency is the accumulated latency divided by the number |
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* of times) |
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*/ |
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#include <linux/kallsyms.h> |
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#include <linux/seq_file.h> |
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#include <linux/notifier.h> |
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#include <linux/spinlock.h> |
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#include <linux/proc_fs.h> |
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#include <linux/latencytop.h> |
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#include <linux/export.h> |
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#include <linux/sched.h> |
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#include <linux/sched/debug.h> |
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#include <linux/sched/stat.h> |
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#include <linux/list.h> |
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#include <linux/stacktrace.h> |
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static DEFINE_RAW_SPINLOCK(latency_lock); |
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#define MAXLR 128 |
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static struct latency_record latency_record[MAXLR]; |
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int latencytop_enabled; |
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void clear_tsk_latency_tracing(struct task_struct *p) |
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{ |
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unsigned long flags; |
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raw_spin_lock_irqsave(&latency_lock, flags); |
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memset(&p->latency_record, 0, sizeof(p->latency_record)); |
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p->latency_record_count = 0; |
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raw_spin_unlock_irqrestore(&latency_lock, flags); |
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} |
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static void clear_global_latency_tracing(void) |
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{ |
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unsigned long flags; |
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raw_spin_lock_irqsave(&latency_lock, flags); |
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memset(&latency_record, 0, sizeof(latency_record)); |
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raw_spin_unlock_irqrestore(&latency_lock, flags); |
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} |
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static void __sched |
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account_global_scheduler_latency(struct task_struct *tsk, |
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struct latency_record *lat) |
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{ |
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int firstnonnull = MAXLR + 1; |
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int i; |
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/* skip kernel threads for now */ |
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if (!tsk->mm) |
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return; |
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for (i = 0; i < MAXLR; i++) { |
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int q, same = 1; |
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/* Nothing stored: */ |
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if (!latency_record[i].backtrace[0]) { |
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if (firstnonnull > i) |
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firstnonnull = i; |
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continue; |
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} |
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for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
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unsigned long record = lat->backtrace[q]; |
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if (latency_record[i].backtrace[q] != record) { |
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same = 0; |
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break; |
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} |
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/* 0 entry marks end of backtrace: */ |
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if (!record) |
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break; |
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} |
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if (same) { |
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latency_record[i].count++; |
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latency_record[i].time += lat->time; |
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if (lat->time > latency_record[i].max) |
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latency_record[i].max = lat->time; |
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return; |
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} |
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} |
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i = firstnonnull; |
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if (i >= MAXLR - 1) |
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return; |
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/* Allocted a new one: */ |
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memcpy(&latency_record[i], lat, sizeof(struct latency_record)); |
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} |
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/** |
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* __account_scheduler_latency - record an occurred latency |
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* @tsk - the task struct of the task hitting the latency |
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* @usecs - the duration of the latency in microseconds |
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* @inter - 1 if the sleep was interruptible, 0 if uninterruptible |
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* |
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* This function is the main entry point for recording latency entries |
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* as called by the scheduler. |
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* |
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* This function has a few special cases to deal with normal 'non-latency' |
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* sleeps: specifically, interruptible sleep longer than 5 msec is skipped |
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* since this usually is caused by waiting for events via select() and co. |
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* |
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* Negative latencies (caused by time going backwards) are also explicitly |
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* skipped. |
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*/ |
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void __sched |
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__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) |
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{ |
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unsigned long flags; |
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int i, q; |
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struct latency_record lat; |
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/* Long interruptible waits are generally user requested... */ |
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if (inter && usecs > 5000) |
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return; |
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/* Negative sleeps are time going backwards */ |
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/* Zero-time sleeps are non-interesting */ |
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if (usecs <= 0) |
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return; |
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memset(&lat, 0, sizeof(lat)); |
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lat.count = 1; |
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lat.time = usecs; |
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lat.max = usecs; |
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stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0); |
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raw_spin_lock_irqsave(&latency_lock, flags); |
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account_global_scheduler_latency(tsk, &lat); |
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for (i = 0; i < tsk->latency_record_count; i++) { |
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struct latency_record *mylat; |
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int same = 1; |
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mylat = &tsk->latency_record[i]; |
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for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
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unsigned long record = lat.backtrace[q]; |
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if (mylat->backtrace[q] != record) { |
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same = 0; |
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break; |
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} |
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/* 0 entry is end of backtrace */ |
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if (!record) |
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break; |
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} |
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if (same) { |
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mylat->count++; |
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mylat->time += lat.time; |
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if (lat.time > mylat->max) |
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mylat->max = lat.time; |
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goto out_unlock; |
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} |
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} |
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/* |
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* short term hack; if we're > 32 we stop; future we recycle: |
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*/ |
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if (tsk->latency_record_count >= LT_SAVECOUNT) |
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goto out_unlock; |
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/* Allocated a new one: */ |
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i = tsk->latency_record_count++; |
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memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); |
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out_unlock: |
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raw_spin_unlock_irqrestore(&latency_lock, flags); |
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} |
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static int lstats_show(struct seq_file *m, void *v) |
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{ |
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int i; |
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seq_puts(m, "Latency Top version : v0.1\n"); |
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for (i = 0; i < MAXLR; i++) { |
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struct latency_record *lr = &latency_record[i]; |
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if (lr->backtrace[0]) { |
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int q; |
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seq_printf(m, "%i %lu %lu", |
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lr->count, lr->time, lr->max); |
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for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
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unsigned long bt = lr->backtrace[q]; |
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if (!bt) |
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break; |
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seq_printf(m, " %ps", (void *)bt); |
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} |
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seq_puts(m, "\n"); |
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} |
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} |
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return 0; |
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} |
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static ssize_t |
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lstats_write(struct file *file, const char __user *buf, size_t count, |
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loff_t *offs) |
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{ |
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clear_global_latency_tracing(); |
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return count; |
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} |
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static int lstats_open(struct inode *inode, struct file *filp) |
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{ |
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return single_open(filp, lstats_show, NULL); |
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} |
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static const struct proc_ops lstats_proc_ops = { |
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.proc_open = lstats_open, |
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.proc_read = seq_read, |
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.proc_write = lstats_write, |
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.proc_lseek = seq_lseek, |
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.proc_release = single_release, |
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}; |
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static int __init init_lstats_procfs(void) |
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{ |
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proc_create("latency_stats", 0644, NULL, &lstats_proc_ops); |
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return 0; |
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} |
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int sysctl_latencytop(struct ctl_table *table, int write, void *buffer, |
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size_t *lenp, loff_t *ppos) |
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{ |
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int err; |
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err = proc_dointvec(table, write, buffer, lenp, ppos); |
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if (latencytop_enabled) |
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force_schedstat_enabled(); |
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return err; |
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} |
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device_initcall(init_lstats_procfs);
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