Date:	Thu, 1 May 2008 01:59:50 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Willy Tarreau <w@....eu>
Cc:	David Miller <davem@...emloft.net>, mingo@...e.hu,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, jirislaby@...il.com
Subject: Re: Slow DOWN, please!!!

On Thursday, 1 of May 2008, Willy Tarreau wrote:
> On Thu, May 01, 2008 at 12:39:01AM +0200, Rafael J. Wysocki wrote:
> > On Thursday, 1 of May 2008, David Miller wrote:
> > > From: Ingo Molnar <mingo@...e.hu>
> > > Date: Thu, 1 May 2008 00:19:36 +0200
> > > 
> > > > The same goes in the other direction as well - you were just hit by 
> > > > scheduler tree related regressions that were only triggered on your 
> > > > 128-way sparc64, but not on our 64way x86 and smaller boxes.
> > > 
> > > You keep saying this over and over again, but the powerpc folks hit
> > > this stuff too.
> > 
> > Well, I think that some changes need some wider testing anyway.
> > 
> > They may be correct from the author's point of view and even from the knowledge
> > and point of view of the maintainer who takes them into his tree.  That's
> > because no one knows everything and it'll always be like this.
> > 
> > Still, with the current process such "suspicious" changes go in as parts of
> > large series of commits and need to be "rediscovered" by the affected testers
> > with the help of bisection.  Moreover, many changes of this kind may go in from
> > many different sources at the same time and that's really problematic.
> 
> That's very true IMHO and is the thing which has been progressively
> appearing since we merge large amounts of code at once. In the "good
> old days", something did not work, the first one to discover it could
> quickly report it on LKML : "hey, my 128-way sparc64 does not boot
> anymore, anybody has any clue", and another one immediately found
> this mail (better signal/noise ratio on LKML at this time) and say
> "oops, I suspect that change, try to revert it".
> 
> Now, it's close to impossible. Maintainers frequently ask for bisection,
> in part because nobody knows what code is merged, and they have to pull
> Linus' tree to know when their changes have been pulled. That may be
> part of the "fun" aspect that Davem is seeing going away in exchange
> for more administrative relations. But if we agree that nobody knows
> all the changes, we must agree that we need tools to track them, and
> tools are fundamentally incompatible with smart human relations.
> 
> > In fact, so many changes go in at a time during a merge window, that we often
> > can't really say which of them causes the breakage observed by testers and
> > bisection, that IMO should really be a last-resort tool, is used on the main
> > debugging techinque.
> 
> Maybe we could slightly improve the process by releasing more often, but
> based on topics. Small sets of minimally-overlapping topics would get
> merged in each release, and other topics would only be allowed to pull
> fixes. That way everybody still gets some work merged, everybody tests
> and problems are more easily spotted.

I like this idea.

> I know this is in part what Andrew tries to do when proposing to
> integrate trees, but maybe some approximate rules should be proposed
> in order for developers to organize their works. This would begin
> with announcing topics to be considered for next branch very early.
> This would also make it more natural for developers to have creation
> and bug-tracking phases.

Yes, that's reasonable.

Thanks,
Rafael
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