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

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Qais Yousef <qyousef@layalina.io>,
	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 13:04:13 -0800	[thread overview]
Message-ID: <CAHk-=whCt-Eem=BbDo+f0VoDerYQNbvnPCdh6fcBNDnLyZyvfA@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wh-RR5DMb8jttBGT3Y+W0=X=dSBHZxWpNECT4Dw0_1erQ@mail.gmail.com>

On Fri, 12 Jan 2024 at 12:49, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> All cores stay at 2.2GHz (ok, so there's noise, but we're
> talking "within a couple of MHz of 2.2GHz").

Note: that is true also when every CPU is fully loaded and I do a real
full build.

So the "empty make" is just my quick test that happens to be
single-threaded and should take just 20s. All my real builds slow down
too, because all CPUs stay at the minimum frequency.

And I just verified that Ingo's revert that only reverts two commits
(commit 60ee1706bd11 in the tip tree), makes things work correctly for
me.

Not surprising, since the bisection clearly pointed at just commit
9c0b4bb7f6303c being the one that caused the issue, but I decided to
just double-check anyway.

So with that revert, for the single-threaded case I see 4GHz+ numbers
(they spread from a single CPU to multiple CPUs once you run the
benchmark a few times).

And then when I run a full parallel build (rather than the
single-threaded empty one), the frequencies drop to ~3.85GHz for the
all-cpu case.

                Linus