linux-kernel - Re: [PATCH] sched/cputime: correct account of irqtime

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Date:   Thu, 15 Oct 2020 09:27:44 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Allen Pais <allen.lkml@...il.com>,
        Romain Perier <romain.perier@...il.com>
Subject: Re: [PATCH] sched/cputime: correct account of irqtime

On Wed, Oct 14, 2020 at 9:02 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Oct 12, 2020 at 09:50:44PM +0800, Pingfan Liu wrote:
> > __do_softirq() may be interrupted by hardware interrupts. In this case,
> > irqtime_account_irq() will account the time slice as CPUTIME_SOFTIRQ by
> > mistake.
> >
> > By passing irqtime_account_irq() an extra param about either hardirq or
> > softirq, irqtime_account_irq() can handle the above case.
>
> I'm not sure I see the scenario in which it goes wrong.
>
> irqtime_account_irq() is designed such that we're called with the old
> preempt_count on enter and the new preempt_count on exit. This way we'll
> accumuate the delta to the previous context.
>
Oops! You are right, the time delta between a softirq and a
interrupting hardirq should be accounted into the softrq.

Thanks for your clear explanation.

Regards,
Pingfan