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

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Message-ID: <20230321100206.GE2234901@hirez.programming.kicks-ass.net>
Date:   Tue, 21 Mar 2023 11:02:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com, dietmar.eggemann@....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 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!