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473 lines
12 KiB
473 lines
12 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* Per Entity Load Tracking |
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* |
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* Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <[email protected]> |
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* |
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* Interactivity improvements by Mike Galbraith |
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* (C) 2007 Mike Galbraith <[email protected]> |
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* |
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* Various enhancements by Dmitry Adamushko. |
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* (C) 2007 Dmitry Adamushko <[email protected]> |
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* |
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* Group scheduling enhancements by Srivatsa Vaddagiri |
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* Copyright IBM Corporation, 2007 |
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* Author: Srivatsa Vaddagiri <[email protected]> |
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* |
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* Scaled math optimizations by Thomas Gleixner |
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* Copyright (C) 2007, Thomas Gleixner <[email protected]> |
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* |
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* Adaptive scheduling granularity, math enhancements by Peter Zijlstra |
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* Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra |
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* |
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* Move PELT related code from fair.c into this pelt.c file |
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* Author: Vincent Guittot <[email protected]> |
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*/ |
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#include <linux/sched.h> |
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#include "sched.h" |
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#include "pelt.h" |
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/* |
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* Approximate: |
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* val * y^n, where y^32 ~= 0.5 (~1 scheduling period) |
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*/ |
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static u64 decay_load(u64 val, u64 n) |
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{ |
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unsigned int local_n; |
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if (unlikely(n > LOAD_AVG_PERIOD * 63)) |
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return 0; |
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/* after bounds checking we can collapse to 32-bit */ |
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local_n = n; |
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/* |
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* As y^PERIOD = 1/2, we can combine |
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* y^n = 1/2^(n/PERIOD) * y^(n%PERIOD) |
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* With a look-up table which covers y^n (n<PERIOD) |
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* |
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* To achieve constant time decay_load. |
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*/ |
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if (unlikely(local_n >= LOAD_AVG_PERIOD)) { |
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val >>= local_n / LOAD_AVG_PERIOD; |
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local_n %= LOAD_AVG_PERIOD; |
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} |
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val = mul_u64_u32_shr(val, runnable_avg_yN_inv[local_n], 32); |
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return val; |
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} |
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static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3) |
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{ |
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u32 c1, c2, c3 = d3; /* y^0 == 1 */ |
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/* |
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* c1 = d1 y^p |
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*/ |
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c1 = decay_load((u64)d1, periods); |
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/* |
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* p-1 |
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* c2 = 1024 \Sum y^n |
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* n=1 |
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* |
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* inf inf |
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* = 1024 ( \Sum y^n - \Sum y^n - y^0 ) |
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* n=0 n=p |
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*/ |
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c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024; |
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return c1 + c2 + c3; |
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} |
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/* |
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* Accumulate the three separate parts of the sum; d1 the remainder |
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* of the last (incomplete) period, d2 the span of full periods and d3 |
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* the remainder of the (incomplete) current period. |
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* |
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* d1 d2 d3 |
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* ^ ^ ^ |
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* | | | |
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* |<->|<----------------->|<--->| |
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* ... |---x---|------| ... |------|-----x (now) |
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* |
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* p-1 |
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* u' = (u + d1) y^p + 1024 \Sum y^n + d3 y^0 |
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* n=1 |
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* |
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* = u y^p + (Step 1) |
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* |
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* p-1 |
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* d1 y^p + 1024 \Sum y^n + d3 y^0 (Step 2) |
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* n=1 |
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*/ |
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static __always_inline u32 |
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accumulate_sum(u64 delta, struct sched_avg *sa, |
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unsigned long load, unsigned long runnable, int running) |
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{ |
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u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */ |
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u64 periods; |
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delta += sa->period_contrib; |
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periods = delta / 1024; /* A period is 1024us (~1ms) */ |
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/* |
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* Step 1: decay old *_sum if we crossed period boundaries. |
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*/ |
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if (periods) { |
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sa->load_sum = decay_load(sa->load_sum, periods); |
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sa->runnable_sum = |
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decay_load(sa->runnable_sum, periods); |
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sa->util_sum = decay_load((u64)(sa->util_sum), periods); |
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/* |
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* Step 2 |
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*/ |
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delta %= 1024; |
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if (load) { |
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/* |
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* This relies on the: |
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* |
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* if (!load) |
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* runnable = running = 0; |
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* |
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* clause from ___update_load_sum(); this results in |
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* the below usage of @contrib to disappear entirely, |
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* so no point in calculating it. |
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*/ |
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contrib = __accumulate_pelt_segments(periods, |
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1024 - sa->period_contrib, delta); |
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} |
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} |
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sa->period_contrib = delta; |
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if (load) |
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sa->load_sum += load * contrib; |
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if (runnable) |
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sa->runnable_sum += runnable * contrib << SCHED_CAPACITY_SHIFT; |
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if (running) |
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sa->util_sum += contrib << SCHED_CAPACITY_SHIFT; |
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return periods; |
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} |
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/* |
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* We can represent the historical contribution to runnable average as the |
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* coefficients of a geometric series. To do this we sub-divide our runnable |
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* history into segments of approximately 1ms (1024us); label the segment that |
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* occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g. |
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* |
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* [<- 1024us ->|<- 1024us ->|<- 1024us ->| ... |
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* p0 p1 p2 |
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* (now) (~1ms ago) (~2ms ago) |
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* |
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* Let u_i denote the fraction of p_i that the entity was runnable. |
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* |
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* We then designate the fractions u_i as our co-efficients, yielding the |
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* following representation of historical load: |
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* u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ... |
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* |
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* We choose y based on the with of a reasonably scheduling period, fixing: |
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* y^32 = 0.5 |
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* |
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* This means that the contribution to load ~32ms ago (u_32) will be weighted |
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* approximately half as much as the contribution to load within the last ms |
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* (u_0). |
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* |
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* When a period "rolls over" and we have new u_0`, multiplying the previous |
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* sum again by y is sufficient to update: |
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* load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... ) |
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* = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}] |
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*/ |
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static __always_inline int |
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___update_load_sum(u64 now, struct sched_avg *sa, |
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unsigned long load, unsigned long runnable, int running) |
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{ |
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u64 delta; |
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delta = now - sa->last_update_time; |
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/* |
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* This should only happen when time goes backwards, which it |
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* unfortunately does during sched clock init when we swap over to TSC. |
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*/ |
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if ((s64)delta < 0) { |
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sa->last_update_time = now; |
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return 0; |
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} |
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/* |
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* Use 1024ns as the unit of measurement since it's a reasonable |
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* approximation of 1us and fast to compute. |
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*/ |
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delta >>= 10; |
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if (!delta) |
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return 0; |
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sa->last_update_time += delta << 10; |
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/* |
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* running is a subset of runnable (weight) so running can't be set if |
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* runnable is clear. But there are some corner cases where the current |
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* se has been already dequeued but cfs_rq->curr still points to it. |
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* This means that weight will be 0 but not running for a sched_entity |
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* but also for a cfs_rq if the latter becomes idle. As an example, |
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* this happens during idle_balance() which calls |
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* update_blocked_averages(). |
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* |
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* Also see the comment in accumulate_sum(). |
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*/ |
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if (!load) |
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runnable = running = 0; |
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/* |
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* Now we know we crossed measurement unit boundaries. The *_avg |
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* accrues by two steps: |
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* |
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* Step 1: accumulate *_sum since last_update_time. If we haven't |
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* crossed period boundaries, finish. |
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*/ |
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if (!accumulate_sum(delta, sa, load, runnable, running)) |
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return 0; |
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return 1; |
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} |
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/* |
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* When syncing *_avg with *_sum, we must take into account the current |
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* position in the PELT segment otherwise the remaining part of the segment |
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* will be considered as idle time whereas it's not yet elapsed and this will |
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* generate unwanted oscillation in the range [1002..1024[. |
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* |
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* The max value of *_sum varies with the position in the time segment and is |
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* equals to : |
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* |
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* LOAD_AVG_MAX*y + sa->period_contrib |
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* |
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* which can be simplified into: |
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* |
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* LOAD_AVG_MAX - 1024 + sa->period_contrib |
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* |
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* because LOAD_AVG_MAX*y == LOAD_AVG_MAX-1024 |
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* |
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* The same care must be taken when a sched entity is added, updated or |
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* removed from a cfs_rq and we need to update sched_avg. Scheduler entities |
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* and the cfs rq, to which they are attached, have the same position in the |
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* time segment because they use the same clock. This means that we can use |
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* the period_contrib of cfs_rq when updating the sched_avg of a sched_entity |
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* if it's more convenient. |
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*/ |
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static __always_inline void |
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___update_load_avg(struct sched_avg *sa, unsigned long load) |
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{ |
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u32 divider = get_pelt_divider(sa); |
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/* |
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* Step 2: update *_avg. |
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*/ |
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sa->load_avg = div_u64(load * sa->load_sum, divider); |
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sa->runnable_avg = div_u64(sa->runnable_sum, divider); |
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WRITE_ONCE(sa->util_avg, sa->util_sum / divider); |
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} |
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/* |
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* sched_entity: |
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* |
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* task: |
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* se_weight() = se->load.weight |
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* se_runnable() = !!on_rq |
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* |
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* group: [ see update_cfs_group() ] |
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* se_weight() = tg->weight * grq->load_avg / tg->load_avg |
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* se_runnable() = grq->h_nr_running |
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* |
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* runnable_sum = se_runnable() * runnable = grq->runnable_sum |
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* runnable_avg = runnable_sum |
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* |
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* load_sum := runnable |
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* load_avg = se_weight(se) * load_sum |
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* |
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* cfq_rq: |
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* |
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* runnable_sum = \Sum se->avg.runnable_sum |
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* runnable_avg = \Sum se->avg.runnable_avg |
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* |
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* load_sum = \Sum se_weight(se) * se->avg.load_sum |
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* load_avg = \Sum se->avg.load_avg |
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*/ |
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int __update_load_avg_blocked_se(u64 now, struct sched_entity *se) |
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{ |
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if (___update_load_sum(now, &se->avg, 0, 0, 0)) { |
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___update_load_avg(&se->avg, se_weight(se)); |
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trace_pelt_se_tp(se); |
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return 1; |
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} |
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return 0; |
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} |
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int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se) |
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{ |
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if (___update_load_sum(now, &se->avg, !!se->on_rq, se_runnable(se), |
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cfs_rq->curr == se)) { |
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___update_load_avg(&se->avg, se_weight(se)); |
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cfs_se_util_change(&se->avg); |
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trace_pelt_se_tp(se); |
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return 1; |
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} |
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return 0; |
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} |
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int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq) |
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{ |
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if (___update_load_sum(now, &cfs_rq->avg, |
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scale_load_down(cfs_rq->load.weight), |
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cfs_rq->h_nr_running, |
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cfs_rq->curr != NULL)) { |
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___update_load_avg(&cfs_rq->avg, 1); |
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trace_pelt_cfs_tp(cfs_rq); |
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return 1; |
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} |
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return 0; |
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} |
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/* |
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* rt_rq: |
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* |
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* util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked |
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* util_sum = cpu_scale * load_sum |
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* runnable_sum = util_sum |
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* |
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* load_avg and runnable_avg are not supported and meaningless. |
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* |
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*/ |
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int update_rt_rq_load_avg(u64 now, struct rq *rq, int running) |
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{ |
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if (___update_load_sum(now, &rq->avg_rt, |
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running, |
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running, |
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running)) { |
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___update_load_avg(&rq->avg_rt, 1); |
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trace_pelt_rt_tp(rq); |
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return 1; |
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} |
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return 0; |
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} |
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/* |
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* dl_rq: |
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* |
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* util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked |
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* util_sum = cpu_scale * load_sum |
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* runnable_sum = util_sum |
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* |
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* load_avg and runnable_avg are not supported and meaningless. |
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* |
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*/ |
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int update_dl_rq_load_avg(u64 now, struct rq *rq, int running) |
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{ |
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if (___update_load_sum(now, &rq->avg_dl, |
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running, |
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running, |
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running)) { |
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___update_load_avg(&rq->avg_dl, 1); |
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trace_pelt_dl_tp(rq); |
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return 1; |
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} |
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return 0; |
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} |
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#ifdef CONFIG_SCHED_THERMAL_PRESSURE |
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/* |
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* thermal: |
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* |
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* load_sum = \Sum se->avg.load_sum but se->avg.load_sum is not tracked |
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* |
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* util_avg and runnable_load_avg are not supported and meaningless. |
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* |
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* Unlike rt/dl utilization tracking that track time spent by a cpu |
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* running a rt/dl task through util_avg, the average thermal pressure is |
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* tracked through load_avg. This is because thermal pressure signal is |
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* time weighted "delta" capacity unlike util_avg which is binary. |
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* "delta capacity" = actual capacity - |
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* capped capacity a cpu due to a thermal event. |
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*/ |
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int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity) |
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{ |
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if (___update_load_sum(now, &rq->avg_thermal, |
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capacity, |
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capacity, |
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capacity)) { |
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___update_load_avg(&rq->avg_thermal, 1); |
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trace_pelt_thermal_tp(rq); |
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return 1; |
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} |
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return 0; |
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} |
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#endif |
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#ifdef CONFIG_HAVE_SCHED_AVG_IRQ |
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/* |
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* irq: |
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* |
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* util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked |
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* util_sum = cpu_scale * load_sum |
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* runnable_sum = util_sum |
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* |
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* load_avg and runnable_avg are not supported and meaningless. |
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* |
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*/ |
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int update_irq_load_avg(struct rq *rq, u64 running) |
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{ |
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int ret = 0; |
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/* |
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* We can't use clock_pelt because irq time is not accounted in |
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* clock_task. Instead we directly scale the running time to |
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* reflect the real amount of computation |
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*/ |
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running = cap_scale(running, arch_scale_freq_capacity(cpu_of(rq))); |
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running = cap_scale(running, arch_scale_cpu_capacity(cpu_of(rq))); |
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/* |
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* We know the time that has been used by interrupt since last update |
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* but we don't when. Let be pessimistic and assume that interrupt has |
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* happened just before the update. This is not so far from reality |
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* because interrupt will most probably wake up task and trig an update |
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* of rq clock during which the metric is updated. |
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* We start to decay with normal context time and then we add the |
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* interrupt context time. |
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* We can safely remove running from rq->clock because |
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* rq->clock += delta with delta >= running |
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*/ |
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ret = ___update_load_sum(rq->clock - running, &rq->avg_irq, |
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0, |
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0, |
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0); |
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ret += ___update_load_sum(rq->clock, &rq->avg_irq, |
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1, |
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1, |
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1); |
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if (ret) { |
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___update_load_avg(&rq->avg_irq, 1); |
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trace_pelt_irq_tp(rq); |
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} |
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return ret; |
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} |
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#endif
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