linux-kernel - Re: [patch] CFS scheduler, -v6

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Message-ID: <4d8e3fd30704290509r79b7fc47i17ce286a43564259@mail.gmail.com>
Date:	Sun, 29 Apr 2007 14:09:14 +0200
From:	"Paolo Ciarrocchi" <paolo.ciarrocchi@...il.com>
To:	"Con Kolivas" <kernel@...ivas.org>
Cc:	"Willy Tarreau" <w@....eu>, "Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Kasper Sandberg" <lkml@...anurb.dk>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Gene Heskett" <gene.heskett@...il.com>,
	linux-kernel@...r.kernel.org, "Nick Piggin" <npiggin@...e.de>,
	"Mike Galbraith" <efault@....de>,
	"Arjan van de Ven" <arjan@...radead.org>,
	"Peter Williams" <pwil3058@...pond.net.au>, caglar@...dus.org.tr,
	"Mark Lord" <lkml@....ca>, "Zach Carter" <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>
Subject: Re: [patch] CFS scheduler, -v6

On 4/29/07, Con Kolivas <kernel@...ivas.org> wrote:
> On Sunday 29 April 2007 21:11, Willy Tarreau wrote:
> > On Sun, Apr 29, 2007 at 12:30:54PM +0200, Thomas Gleixner wrote:
> > > Willy,
> > >
> > > On Sun, 2007-04-29 at 09:16 +0200, Willy Tarreau wrote:
> > > > In fact, what I'd like to see in 2.6.22 is something better for
> > > > everybody and with *no* regression, even if it's not perfect. I had the
> > > > feeling that SD matched that goal right now, except for Mike who has
> > > > not tested recent versions. Don't get me wrong, I still think that CFS
> > > > is a more interesting long-term target. But it may require more time to
> > > > satisfy everyone. At least with one of them in 2.6.22, we won't waste
> > > > time comparing to current mainline.
> > >
> > > Oh no, we really do _NOT_ want to throw SD or anything else at mainline
> > > in a hurry just for not wasting time on comparing to the current
> > > scheduler.
> >
> > It is not about doing it in a hurry. I see SD as a small yet efficient
> > update to current scheduler. It's not perfect, probably not much extensible
> > but the risks of breaking anything are small given the fact that it does
> > not change much of the code or behaviour.
> >
> > IMHO, it is something which can provide users with a useful update while
> > leaving us with some more time to carefully implement the features of CFS
> > one at a time, and if it requires 5 versions, it's not a problem.
> >
> > > I agree that CFS is the more interesting target and I prefer to push the
> > > more interesting one even if it takes a release cycle longer. The main
> > > reason for me is the design of CFS. Even if it is not really modular
> > > right now, it is not rocket science to make it fully modular.
> > >
> > > Looking at the areas where people work on, e.g. containers, resource
> > > management, cpu isolation, fully tickless systems ...., we really need
> > > to go into that direction, when we want to avoid permanent tinkering in
> > > the core scheduler code for the next five years.
> > >
> > > As a sidenote: I really wonder if anybody noticed yet, that the whole
> > > CFS / SD comparison is so ridiculous, that it is not even funny anymore.
> >
> > Contrarily to most people, I don't see them as competitors. I see SD as
> > a first step with a low risk of regression, and CFS as an ultimate
> > solution relying on a more solid framework.
> >
> > > CFS modifies the scheduler and nothing else, SD fiddles all over the
> > > kernel in interesting ways.
> >
> > Hmmm I guess you confused both of them this time. CFS touches many places,
> > which is why I think the testing coverage is still very low. SD can be
> > tested faster. My real concern is : are there still people observing
> > regressions with it ? If yes, they should be fixed before even being
> > merged. If no, why not merge it as a fix for the many known corner cases
> > of current scheduler ? After all, it's already in -mm.
> >
> > Willy
>
> Willy, you're making far too much sense. Are you replying to the correct
> mailing list?

FWIW, I strongly agree with Willy.

Ciao,
-- 
Paolo
"Tutto cio' che merita di essere fatto,merita di essere fatto bene"
Philip Stanhope IV conte di Chesterfield
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