linux-kernel - Re: [GIT PULL] Scheduler changes for v6.8

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Date: Sat, 13 Jan 2024 18:37:55 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Juri Lelli <juri.lelli@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8

On 01/12/24 17:24, Linus Torvalds wrote:
> On Fri, 12 Jan 2024 at 17:04, Qais Yousef <qyousef@...alina.io> wrote:
> >
> > That is odd. I can't see how the patch can cause this yet, could you try with
> > a different compiler if possible?
> 
> I use two different compilers - I do my allmodconfig builds with gcc,
> and the kernels I boot with clang, so my problems have been with a
> kernel built with
> 
>    clang version 17.0.6
> 
> but to check that it's not a compiler issue I just did another try
> with my current public tip of tree (ie *without* any reverts for this
> issue) and gcc:
> 
>     gcc version 13.2.1
> 
> and the behavior is exactly the same: all cores are stuck at 2.2GHz.
> 
> So no, it's not compiler-dependent.
> 
> > I usually use perfetto but it should be easy to see frequency updates from
> > power/cpu_frequency trace event.
> >
> >         echo 1 | sudo tee /sys/kernel/tracing/tracing_on
> >         echo 1 | sudo tee /sys/kernel/tracing/events/power/cpu_frequency/enable
> >         sudo cat /sys/kernel/tracing/trace
> 
> Shows absolutely nothing. Or rather, it shows the header with
> 
>   # entries-in-buffer/entries-written: 0/0   #P:64
> 
> and that's it.
> 
> With a *working* kernel, I get events, setting the frequency to either
> 2.2GHz (idle) or 3.8GHz (work).
> 
> IOW, the tracing output is 100% consistent with "that commit breaks everything".

Thanks for all the info. It seems for some reason we no longer think we need to
update the frequency. Not sure why yet. It's strange I can't reproduce too even
running from top of your tree. I ran with these patches on M1, Pixel, Intel and
now AMD and haven't noticed anything since they got merged.