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Message-ID: <Znx-0ksd-Be3YC1C@slm.duckdns.org>
Date: Wed, 26 Jun 2024 10:49:22 -1000
From: Tejun Heo <tj@...nel.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>, torvalds@...ux-foundation.org,
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Subject: Re: [PATCH 10/39] sched: Factor out update_other_load_avgs() from
__update_blocked_others()
Hello,
On Tue, Jun 25, 2024 at 11:13:54AM +0200, Vincent Guittot wrote:
> > Hmm.... I think I saw RT's schedutil signal stuck high constantly pushing up
> > the frequency. I might be mistaken tho. I'll check again.
>
> This is used when selecting a frequency for fair tasks
When schedutil is used as the governor, sugov_get_util() provides the source
utilization information to determine the target frequency. sugov_get_util()
gets the CFS util metric from cpu_util_cfs_boost() and then runs it through
effective_cpu_util().
effective_cpu_util() does a bunch of things including adding cpu_util_irq(),
cpu_util_rt() and cpu_util_dl(), so if SCX doesn't decay these utilization
metrics, they never decay and schedutil ends up making decisions with stale
stuck-high numbers. I can easily confirm the behavior by sprinkling some
trace_printks and commenting out update_other_load_avgs() on the SCX side.
Thanks.
--
tejun
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