linux-kernel - Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated

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Message-ID: <7bba69e0-5261-9921-16b7-c8592b5d213b@arm.com>
Date:   Tue, 21 Mar 2023 11:29:13 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org,
        zhangqiao22@...wei.com
Subject: Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated

On 21/03/2023 11:02, Peter Zijlstra wrote:
> On Fri, Mar 17, 2023 at 05:08:10PM +0100, Vincent Guittot wrote:
>> Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed")
>> fixes an overflowing bug, but ignore a case that se->exec_start is reset
>> after a migration.
>>
>> For fixing this case, we delay the reset of se->exec_start after
>> placing the entity which se->exec_start to detect long sleeping task.
>>
>> In order to take into account a possible divergence between the clock_task
>> of 2 rqs, we increase the threshold to around 104 days.
>>
>>
>> Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed")
>> Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
> 
> Blergh, this just isn't going to be nice. I'll go queue this for
> sched/urgent and then we can forget about this for a little while.
> 
> Thanks!

Don't we miss setting `se->exec_start = 0` for fair task in
move_queued_task()? ( ... and __migrate_swap_task())

https://lkml.kernel.org/r/df2cccda-1550-b06b-aa74-e0f054e9fb9d@arm.com