linux-kernel - Re: Potential scheduler regression

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Date:   Tue, 11 Jul 2017 11:55:12 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Ben Guthro <ben@...hro.net>, 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 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