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Message-ID: <CALOAHbAmQ_4c7EuOb-7CT5g10hH12-jYm5_1joeWkcADg40g0g@mail.gmail.com>
Date: Wed, 4 Dec 2024 10:23:01 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, 
	vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, hannes@...xchg.org, 
	surenb@...gle.com, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/4] sched, psi: Don't account irq time if
 sched_clock_irqtime is disabled

On Tue, Dec 3, 2024 at 6:15 PM Michal Koutný <mkoutny@...e.com> wrote:
>
> On Tue, Dec 03, 2024 at 11:01:41AM GMT, Michal Koutný <mkoutny@...e.com> wrote:
> > On Fri, Nov 08, 2024 at 09:29:03PM GMT, Yafang Shao <laoar.shao@...il.com> wrote:
> > > sched_clock_irqtime may be disabled due to the clock source. When disabled,
> > > irq_time_read() won't change over time, so there is nothing to account. We
> > > can save iterating the whole hierarchy on every tick and context switch.
> > >
> > > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > > Acked-by: Johannes Weiner <hannes@...xchg.org>
> > > ---
> > >  kernel/sched/psi.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Reviewed-by: Michal Koutný <mkoutny@...e.com>
>
> On second thought, similar guard may be useful in psi_show() too. Since
> there's a difference between zero pressure and unmeasured pressure (it'd
> fail with EOPNOTSUPP).

I'll update the psi_show() function in the next version.

>
> (How common is it actually that tsc_init fails?)

This is not a common scenario, but it can occur randomly across a large fleet.

--
Regards
Yafang

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