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

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Message-ID: <ebf5c056-3035-4e76-9472-d76be6427669@leemhuis.info>
Date: Sun, 9 Jun 2024 10:11:02 +0200
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@...mhuis.info>
To: David Laight <David.Laight@...lab.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Linux kernel regressions list <regressions@...ts.linux.dev>
Subject: Re: Linux 6.10-rc2 - massive performance regression

On 09.06.24 00:00, Linus Torvalds wrote:
> On Sat, 8 Jun 2024 at 14:36, David Laight <David.Laight@...lab.com> wrote:
> [...]
>> 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.

David, what kind of hardware do you use? Johan Hovold as
man-in-the-middle just reported "CPU frequency of the big cores on the
Lenovo ThinkPad X13s sometimes appears to get stuck at a low frequency
with 6.10-rc2" and confirmed "that once the cores are fully throttled
(using the stepwise thermal governor) due to the skin temperature
reaching the
first trip point, scaling_max_freq gets stuck at the next OPP".

For more details, see:
https://lore.kernel.org/all/ZmVfcEOxmjUHZTSX@hovoldconsulting.com/

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

Sadly that one is not bisected yet either. :-/

Ciao, Thorsten