From: "tip-bot2 for Vincent Donnefort" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Vincent Donnefort <vincent.donnefort@arm.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/core] sched/pelt: Fix task util_est update filtering
Date: Tue, 02 Mar 2021 09:01:53 -0000 [thread overview]
Message-ID: <161467571313.20312.15038031807589971207.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210225165820.1377125-1-vincent.donnefort@arm.com>
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 78ca1ab2718a5518171f2e7d0afad0b9752c4453
Gitweb: https://git.kernel.org/tip/78ca1ab2718a5518171f2e7d0afad0b9752c4453
Author: Vincent Donnefort <vincent.donnefort@arm.com>
AuthorDate: Thu, 25 Feb 2021 16:58:20
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 01 Mar 2021 18:17:26 +01:00
sched/pelt: Fix task util_est update filtering
Being called for each dequeue, util_est reduces the number of its updates
by filtering out when the EWMA signal is different from the task util_avg
by less than 1%. It is a problem for a sudden util_avg ramp-up. Due to the
decay from a previous high util_avg, EWMA might now be close enough to
the new util_avg. No update would then happen while it would leave
ue.enqueued with an out-of-date value.
Taking into consideration the two util_est members, EWMA and enqueued for
the filtering, ensures, for both, an up-to-date value.
This is for now an issue only for the trace probe that might return the
stale value. Functional-wise, it isn't a problem, as the value is always
accessed through max(enqueued, ewma).
This problem has been observed using LISA's UtilConvergence:test_means on
the sd845c board.
No regression observed with Hackbench on sd845c and Perf-bench sched pipe
on hikey/hikey960.
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210225165820.1377125-1-vincent.donnefort@arm.com
---
kernel/sched/fair.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1af51a6..f5d6541 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3941,6 +3941,8 @@ static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
trace_sched_util_est_cfs_tp(cfs_rq);
}
+#define UTIL_EST_MARGIN (SCHED_CAPACITY_SCALE / 100)
+
/*
* Check if a (signed) value is within a specified (unsigned) margin,
* based on the observation that:
@@ -3958,7 +3960,7 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
struct task_struct *p,
bool task_sleep)
{
- long last_ewma_diff;
+ long last_ewma_diff, last_enqueued_diff;
struct util_est ue;
if (!sched_feat(UTIL_EST))
@@ -3979,6 +3981,8 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
if (ue.enqueued & UTIL_AVG_UNCHANGED)
return;
+ last_enqueued_diff = ue.enqueued;
+
/*
* Reset EWMA on utilization increases, the moving average is used only
* to smooth utilization decreases.
@@ -3992,12 +3996,17 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
}
/*
- * Skip update of task's estimated utilization when its EWMA is
+ * Skip update of task's estimated utilization when its members are
* already ~1% close to its last activation value.
*/
last_ewma_diff = ue.enqueued - ue.ewma;
- if (within_margin(last_ewma_diff, (SCHED_CAPACITY_SCALE / 100)))
+ last_enqueued_diff -= ue.enqueued;
+ if (within_margin(last_ewma_diff, UTIL_EST_MARGIN)) {
+ if (!within_margin(last_enqueued_diff, UTIL_EST_MARGIN))
+ goto done;
+
return;
+ }
/*
* To avoid overestimation of actual task utilization, skip updates if
next prev parent reply other threads:[~2021-03-02 9:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 16:58 [PATCH v2] sched/pelt: Fix task util_est update filtering Vincent Donnefort
2021-02-26 7:22 ` Vincent Guittot
2021-02-26 8:41 ` Peter Zijlstra
2021-03-01 16:34 ` Dietmar Eggemann
2021-03-01 17:21 ` Peter Zijlstra
2021-03-03 10:06 ` Vincent Donnefort
2021-03-02 9:01 ` tip-bot2 for Vincent Donnefort [this message]
2021-03-03 9:49 ` [tip: sched/core] " tip-bot2 for Vincent Donnefort
2021-03-06 11:42 ` tip-bot2 for Vincent Donnefort
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