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authorDietmar Eggemann <dietmar.eggemann@arm.com>2021-06-02 16:58:08 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-06-03 15:47:23 +0200
commit68d7a190682aa4eb02db477328088ebad15acc83 (patch)
treeb69fb60b812faf894f79fb38fb3e9896ab01c958 /kernel/sched/pelt.h
parentfcf6631f3736985ec89bdd76392d3c7bfb60119f (diff)
sched/fair: Fix util_est UTIL_AVG_UNCHANGED handling
The util_est internal UTIL_AVG_UNCHANGED flag which is used to prevent unnecessary util_est updates uses the LSB of util_est.enqueued. It is exposed via _task_util_est() (and task_util_est()). Commit 92a801e5d5b7 ("sched/fair: Mask UTIL_AVG_UNCHANGED usages") mentions that the LSB is lost for util_est resolution but find_energy_efficient_cpu() checks if task_util_est() returns 0 to return prev_cpu early. _task_util_est() returns the max value of util_est.ewma and util_est.enqueued or'ed w/ UTIL_AVG_UNCHANGED. So task_util_est() returning the max of task_util() and _task_util_est() will never return 0 under the default SCHED_FEAT(UTIL_EST, true). To fix this use the MSB of util_est.enqueued instead and keep the flag util_est internal, i.e. don't export it via _task_util_est(). The maximal possible util_avg value for a task is 1024 so the MSB of 'unsigned int util_est.enqueued' isn't used to store a util value. As a caveat the code behind the util_est_se trace point has to filter UTIL_AVG_UNCHANGED to see the real util_est.enqueued value which should be easy to do. This also fixes an issue report by Xuewen Yan that util_est_update() only used UTIL_AVG_UNCHANGED for the subtrahend of the equation: last_enqueued_diff = ue.enqueued - (task_util() | UTIL_AVG_UNCHANGED) Fixes: b89997aa88f0b sched/pelt: Fix task util_est update filtering Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Xuewen Yan <xuewen.yan@unisoc.com> Reviewed-by: Vincent Donnefort <vincent.donnefort@arm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lore.kernel.org/r/20210602145808.1562603-1-dietmar.eggemann@arm.com
Diffstat (limited to 'kernel/sched/pelt.h')
-rw-r--r--kernel/sched/pelt.h11
1 files changed, 1 insertions, 10 deletions
diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h
index 1462846d244e..cfe94ffd2b38 100644
--- a/kernel/sched/pelt.h
+++ b/kernel/sched/pelt.h
@@ -42,15 +42,6 @@ static inline u32 get_pelt_divider(struct sched_avg *avg)
return LOAD_AVG_MAX - 1024 + avg->period_contrib;
}
-/*
- * When a task is dequeued, its estimated utilization should not be update if
- * its util_avg has not been updated at least once.
- * This flag is used to synchronize util_avg updates with util_est updates.
- * We map this information into the LSB bit of the utilization saved at
- * dequeue time (i.e. util_est.dequeued).
- */
-#define UTIL_AVG_UNCHANGED 0x1
-
static inline void cfs_se_util_change(struct sched_avg *avg)
{
unsigned int enqueued;
@@ -58,7 +49,7 @@ static inline void cfs_se_util_change(struct sched_avg *avg)
if (!sched_feat(UTIL_EST))
return;
- /* Avoid store if the flag has been already set */
+ /* Avoid store if the flag has been already reset */
enqueued = avg->util_est.enqueued;
if (!(enqueued & UTIL_AVG_UNCHANGED))
return;