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

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Qais Yousef <qyousef@layalina.io>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	 Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org,
	 Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	 Juri Lelli <juri.lelli@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	 Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	 Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8
Date: Fri, 12 Jan 2024 17:24:50 -0800	[thread overview]
Message-ID: <CAHk-=wgfS+F+QNbFPurhnZTVLkw4xDOmmaSD3qdQLUoE2VsGTw@mail.gmail.com> (raw)
In-Reply-To: <20240113010432.xe25lxqogxuvl72t@airbuntu>

On Fri, 12 Jan 2024 at 17:04, Qais Yousef <qyousef@layalina.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".

                  Linus