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Subject: Re: [External] Re: [PATCH] psi: Remove the redundant psi_task_tick
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, rostedt@goodmis.org,
        dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org
References: <20210207115642.75620-1-zhouchengming@bytedance.com>
 <YCFqxEw0wJC6UGiE@cmpxchg.org>
From:   Chengming Zhou <zhouchengming@bytedance.com>
Message-ID: <1165c0f2-134e-932d-e427-3b65c659108d@bytedance.com>
Date:   Tue, 9 Feb 2021 10:21:22 +0800
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在 2021/2/9 上午12:45, Johannes Weiner 写道:

> On Sun, Feb 07, 2021 at 07:56:42PM +0800, Chengming Zhou wrote:
>> From: zhouchengming <zhouchengming@bytedance.com>
>>
>> When the current task in a cgroup is in_memstall, the corresponding psi_group
>> is in PSI_MEM_FULL state
> This is correct.
>
>> so we can remove the redundant psi_task_tick from scheduler_tick to
>> save this periodic cost.
> But this isn't. It IS the task tick that makes it so. The state change
> tracking counts MEMSTALL tasks and ONCPU tasks, but it doesn't check
> whether the ONCPU task is the MEMSTALL one.

Yes, you are right, I messed them up... will take a closer look at the code later.

Thanks.

> It would be possible to incorporate that into psi_task_switch(), but
> you have to be careful with the branches because that path is often
> hotter than the timer tick.
>
> This patch by itself breaks page reclaim detection, so NAK.