linux-kernel - Re: Potential scheduler regression

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Date:   Tue, 11 Jul 2017 10:30:14 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Ben Guthro <ben@...hro.net>
Cc:     Greg KH <gregkh@...uxfoundation.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


* 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.

Thanks,

	Ingo