Re: Linux 6.10-rc2 - massive performance regression

[Woody Suwalski]

Linus Torvalds wrote:
> On Sat, 8 Jun 2024 at 14:36, David Laight <David.Laight@xxxxxxxxxx> 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
I have run a quick test on my laptop doing

time (i=0; while [ $i -lt 1000000 ]; do i=$((i+1)); done)

and 6.8.12, 6.9.3 and 6.10-rc2 have identical results...

Woody