linux-kernel - Re: Linux 6.10-rc2 - massive performance regression

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Date: Sat, 8 Jun 2024 15:00:43 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Laight <David.Laight@...lab.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 6.10-rc2 - massive performance regression

On Sat, 8 Jun 2024 at 14:36, David Laight <David.Laight@...lab.com> wrote:
>
> I'll try to remember how to bisect through the merge :-)

git bisect should just do all the work for you. All you need to do is
give a know good and bad point, and keep testing what git bisect asks
you to do.

> I've done some tests.
> I'm seeing a three-fold slow down on:
> $ i=0; while [ $i -lt 1000000 ]; do i=$((i + 1)); done
> which goes from 1 second to 3.
>
> I can run that with ftrace monitoring scheduler events (and a few
> other things) and can't spot anywhere the process isn't running
> for a significant time.

Sounds like cpu frequency. Almost certainly hw-specific. I went
through that on my Threadripper in the 6.9 timeframe, but I'm not
seeing any issues in this current release.

If you bisect it, we have somebody to blame and point fingers at...

                Linus