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Date:   Fri, 1 Dec 2023 08:32:40 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Yuanhan Zhang <zyhtheonly@gmail.com>
Cc:     rostedt@goodmis.org, tglx@linutronix.de, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, linux-kernel@vger.kernel.org,
        dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, zyhtheonly@yeah.net
Subject: Re: [PATCH v2] sched/cputime: exclude ktimers threads in
 irqtime_account_irq
Message-ID: <20231201073240.T9bFNCkU@linutronix.de>
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On 2023-12-01 15:27:39 [+0800], Yuanhan Zhang wrote:
> Hi Sebastian, thanks for your reply.
Hi,

> Sebastian Andrzej Siewior <bigeasy@linutronix.de> =E4=BA=8E2023=E5=B9=B41=
1=E6=9C=8830=E6=97=A5=E5=91=A8=E5=9B=9B 20:00=E5=86=99=E9=81=93=EF=BC=9A
> >
> > 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)?
>=20
> 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?
>=20
> 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