linux-kernel - Re: [PATCH] sched/tracing: correct the task blocking state

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Date: Tue, 02 Jan 2024 17:16:22 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Alex Shi <seakeel@...il.com>
Cc: alexs@...nel.org, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra
 <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent
 Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann
 <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben
 Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot
 de Oliveira <bristot@...hat.com>, linux-kernel@...r.kernel.org,
 curuwang@...cent.com
Subject: Re: [PATCH] sched/tracing: correct the task blocking state

On 02/01/24 21:00, Alex Shi wrote:
> On Tue, Jan 2, 2024 at 6:19 PM Valentin Schneider <vschneid@...hat.com> wrote:
>>
>> On 02/01/24 15:33, alexs@...nel.org wrote:
>> > From: Alex Shi <alexs@...nel.org>
>> >
>> > commit 80ed87c8a9ca ("sched/wait: Introduce TASK_NOLOAD and TASK_IDLE")
>> > stopped the idle kthreads contribution to loadavg. Also task idle should
>> > separated from blocked state too, otherwise we will get incorrect task
>> > blocking state from event tracing sched:sched_stat_blocked.
>> >
>>
>> Why is that incorrect? AFAICT we have mapped the (schedstat) 'blocked'
>> meaning to TASK_UNINTERRUPTIBLE. TASK_IDLE tasks don't contribute to
>> loadavg yes, but they are still in an UNINTERRUPTIBLE wait.
>
>
> Hi Valentin,
> Thanks a lot for the reply.
>
> I agree with you the current usage, but if so, we account for the idle task into
> blocked state. And it's better to distinguish between idle and block.
>

Why is that an issue? If those tasks didn't have to be
TASK_UNINTERRUPTIBLE (via TASK_IDLE), we'd make them TASK_INTERRUPTIBLE and
they'd also inflate the 'sleeping' schedstat (rather than the 'blocked').

What problem are you facing with those tasks being flagged as blocked during
their wait?