linux-kernel - Re: [PATCH 13/15] x86/kconfig/64: Enable popular scheduler, cgroups and namespaces options in the defconfig

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Message-ID: <CALOAHbDw1uw-MTYSCk7t22HdVuxwvHgs_FT8f2pvH1GsdGrh4A@mail.gmail.com>
Date: Thu, 22 May 2025 13:49:50 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, ardb@...nel.org, arnd@...db.de, bp@...en8.de, 
	dwmw@...zon.co.uk, hpa@...or.com, linux-kernel@...r.kernel.org, 
	michal.lkml@...kovi.net, tglx@...utronix.de, torvalds@...ux-foundation.org, 
	vkuznets@...hat.com, yamada.masahiro@...ionext.com
Subject: Re: [PATCH 13/15] x86/kconfig/64: Enable popular scheduler, cgroups
 and namespaces options in the defconfig

On Thu, May 8, 2025 at 12:23 AM Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Yafang Shao <laoar.shao@...il.com> wrote:
>
> > On Wed, May 7, 2025 at 3:06 PM Ingo Molnar <mingo@...nel.org> wrote:
> > >
> > >
> > > * Yafang Shao <laoar.shao@...il.com> wrote:
> > >
> > > > Hello Mingo,
> > > >
> > > > > +CONFIG_VIRT_CPU_ACCOUNTING_GEN=y
> > > > > +CONFIG_IRQ_TIME_ACCOUNTING=y
> > > >
> > > > Enabling CONFIG_IRQ_TIME_ACCOUNTING=y can lead to user-visible behavioral
> > > > changes. For more context, please refer to the related discussion here:
> > > > https://lore.kernel.org/all/20241222024734.63894-1-laoar.shao@gmail.com/ .
> > >
> > > Yeah. I actually agree with your series. It (re-)includes IRQ/softirq
> > > time in task CPU usage statistics even under IRQ_TIME_ACCOUNTING=y,
> > > while still keeping the finegrained IRQ/softirq statistics as well,
> > > correct?
> >
> > Correct.
> >
> > >
> > > The Kconfig option is also arguably rather misleading:
> > >
> > > config IRQ_TIME_ACCOUNTING
> > >         bool "Fine granularity task level IRQ time accounting"
> > >         depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
> > >         help
> > >           Select this option to enable fine granularity task irq time
> > >           accounting. This is done by reading a timestamp on each
> > >           transitions between softirq and hardirq state, so there can be a
> > >           small performance impact.
> > >
> > > It only warns about a small performance impact, but doesn't warn that
> > > CPU accounting is changed in an incompatible fashion that surprises
> > > tooling...
> >
> > Yes, this breaks our userspace tools.
>
> Okay, so 2 out of your 3 fixes are upstream already:
>
>   763a744e24a8 ("sched: Don't account irq time if sched_clock_irqtime is disabled")
>   a6fd16148fdd ("sched, psi: Don't account irq time if sched_clock_irqtime is disabled")
>
> But we don't have this one yet:
>
>   [PATCH v8 4/4] sched: Fix cgroup irq time for CONFIG_IRQ_TIME_ACCOUNTING
>
>   https://lore.kernel.org/r/20250103022409.2544-5-laoar.shao@gmail.com
>
> which is also essential to fully fix the tooling regression, right?
>
> I think this last patch fell between the cracks, I didn't see any
> fundamental objections against the fix.
>
> Since the patch does not apply cleanly anymore, mind sending a fresh
> -v9 version against v6.15-rc5 or so?

Hello Ingo,

I have sent the v9:
https://lore.kernel.org/all/20250511030800.1900-1-laoar.shao@gmail.com/

Could you please help review this? I’d appreciate your feedback.

-- 
Regards
Yafang