linux-kernel - Re: Potential scheduler regression

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Date:   Fri, 14 Jul 2017 08:54:07 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ben Guthro <ben@...hro.net>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Potential scheduler regression

On Thu, Jul 13, 2017 at 03:24:02PM -0400, Ben Guthro wrote:
> On Tue, Jul 11, 2017 at 5:55 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Tue, Jul 11, 2017 at 10:30:14AM +0200, Ingo Molnar wrote:
> >>
> >> * Ben Guthro <ben@...hro.net> wrote:
> >>
> >> > > If people have experience with these in the "enterprise" distros, or any other
> >> > > tree, and want to provide me with backported, and tested, patches, I'll be
> >> > > glad to consider them for stable kernels.
> >> > >
> >> > > thanks,
> >> > >
> >> > > greg k-h
> >> >
> >> > I tried to do a simple cherry-pick of the suggested patches - but they
> >> > apply against files that don't exist in the 4.9 series.
> >>
> >> I think there are only two strategies to maintain a backport which work in the
> >> long run:
> >>
> >>  - insist on the simplest fixes and pure cherry-picks
> >>
> >>  - or pick up _everything_ to sync up the two versions.
> >>
> >> The latter would mean a lot of commits - and I'm afraid it would also involve the
> >> scheduler header split-up, which literally involves hundreds of files plus
> >> perpetual build-breakage risk, so it's a no-no.
> >>
> >> > In my release of 4.9 - I'm planning on doing the simpler revert of 1b568f0aab
> >> > that introduced the performance degradation, rather than pulling in lots of code
> >> > from newer kernels.
> >>
> >> That sounds much saner - I'd even Ack that approach for -stable as a special
> >> exception, than to complicate things with excessive backports.
> >
> > Ok, I'll revert that for the next stable release after this one that is
> > currently under review.
> >
> > thanks,
> >
> > greg k-h
> 
> Greg,
> 
> Just for clarity - is the "next one" 4.9.38 (posted today for review)
> - or the one following?

Doh, I forgot it for this release, sorry about that, will try to get to
it for the next one after this.

greg k-h