linux-kernel - Re: [PATCH v2 2/4] psi: Use ONCPU state tracking machinery to detect reclaim

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Date:   Wed, 3 Mar 2021 16:52:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     hannes@...xchg.org, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com
Subject: Re: [PATCH v2 2/4] psi: Use ONCPU state tracking machinery to detect
 reclaim

On Wed, Mar 03, 2021 at 11:46:57AM +0800, Chengming Zhou wrote:
> Move the reclaim detection from the timer tick to the task state
> tracking machinery using the recently added ONCPU state. And we
> also add task psi_flags changes checking in the psi_task_switch()
> optimization to update the parents properly.
> 
> In terms of performance and cost, this ONCPU task state tracking
> is not cheaper than previous timer tick in aggregate. But the code is
> simpler and shorter this way, so it's a maintainability win. And
> Johannes did some testing with perf bench, the performace and cost
> changes would be acceptable for real workloads.
> 
> Thanks to Johannes Weiner for pointing out the psi_task_switch()
> optimization things and the clearer changelog.
> 
Co-developed-by: Muchun ?
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>