linux-kernel - Re: [bug-report] possible s64 overflow in max

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Message-ID: <Y9O5Fwfib2CVAMwl@hirez.programming.kicks-ass.net>
Date:   Fri, 27 Jan 2023 12:44:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Roman Kagan <rkagan@...zon.de>,
        Zhang Qiao <zhangqiao22@...wei.com>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        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>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [bug-report] possible s64 overflow in max_vruntime()

On Thu, Jan 26, 2023 at 07:31:02PM +0100, Roman Kagan wrote:

> > All that only matters for small sleeps anyway.
> > 
> > Something like:
> > 
> >         sleep_time = U64_MAX;
> >         if (se->avg.last_update_time)
> >           sleep_time = cfs_rq_clock_pelt(cfs_rq) - se->avg.last_update_time;
> 
> Interesting, why not rq_clock_task(rq_of(cfs_rq)) - se->exec_start, as
> others were suggesting?  It appears to better match the notion of sleep
> wall-time, no?

Should also work I suppose. cfs_rq_clock takes throttling into account,
but that should hopefully also not be *that* long, so either should
work.