linux-kernel - Re: [PATCH v2] sched/cputime: exclude ktimers threads in irqtime_account

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Message-ID: <20231201073240.T9bFNCkU@linutronix.de>
Date:   Fri, 1 Dec 2023 08:32:40 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Yuanhan Zhang <zyhtheonly@...il.com>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, zyhtheonly@...h.net
Subject: Re: [PATCH v2] sched/cputime: exclude ktimers threads in
 irqtime_account_irq

On 2023-12-01 15:27:39 [+0800], Yuanhan Zhang wrote:
> Hi Sebastian, thanks for your reply.
Hi,

> Sebastian Andrzej Siewior <bigeasy@...utronix.de> 于2023年11月30日周四 20:00写道：
> >
> > On 2023-11-30 17:41:47 [+0800], tiozhang wrote:
> > > In CONFIG_PREEMPT_RT kernel, ktimers also calls __do_softirq,
> > > so when accounting CPUTIME_SOFTIRQ, ktimers need to be excluded
> > > as well as ksoftirqd.
> > > Also add this_cpu_ktimers to keep consistency with this_cpu_ksoftirqd.
> >
> > I'm still not sure what the benefit here is. It says align with
> > ksoftirqd but why? Why don't we account softirq time for ksoftirqd (and
> > should continue to do so for ktimersd)?
> 
> That is my miss. When CONFIG_IRQ_TIME_ACCOUNTING is enabled,
> ksoftirqd is counted elsewhere (where ktimers should also be aligned).
> Please review my later patch v3.

What is elsewhere?

> > ktimers runs almost all the time in softirq context. So does every
> > force-threaded interrupt. Should we exclude them, too?
> 
> For force-threaded interrupt, it counts on CPUTIME_SYSTEM
> instead of CPUTIME_IRQ nor CPUTIME_SOFTIRQ.
> To me, it does not quite make sense, I'm also thinking of sending a patch
> of this, but IMHO it should not be considered in this patch...

Sure. I was just curious what is different with ktimers/ksoftirqd which
run mostly in softirq vs threaded interrupts which do the same.

Sebastian