Subject: Re: Which kernel is the best for a small linux system?
From: Mike Galbraith <efault@gmx.de>
To: Willy Tarreau <willy@w.ods.org>
Cc: Ingo Molnar <mingo@elte.hu>, Arjan van de Ven <arjan@infradead.org>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
In-Reply-To: <1142327130.8075.30.camel@homer>
References: <436c596f0603121640h4f286d53h9f1dd177fd0475a4@mail.gmail.com>
	 <1142237867.3023.8.camel@laptopd505.fenrus.org>
	 <opcb12964ic9im9ojmobduqvvu4pcpgppc@4ax.com>
	 <1142273212.3023.35.camel@laptopd505.fenrus.org>
	 <20060314062144.GC21493@w.ods.org>  <20060314072921.GA13969@elte.hu>
	 <1142327130.8075.30.camel@homer>
Content-Type: text/plain
Date: Thu, 16 Mar 2006 16:24:19 +0100
Message-Id: <1142522659.8195.33.camel@homer>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1852
Lines: 38

On Tue, 2006-03-14 at 10:05 +0100, Mike Galbraith wrote:
> On Tue, 2006-03-14 at 08:29 +0100, Ingo Molnar wrote:
> > * Willy Tarreau <willy@w.ods.org> wrote:
> > 
> > > scheduler is still a big problem. Not only we occasionally see people 
> > > complaining about unfair CPU distribution across processes (may be 
> > > fixed now), but the scheduler still gives a huge boost to I/O 
> > > intensive tasks which do lots of select() with small time-outs, which 
> > > makes it practically unusable in network-intensive environments. I've 
> > > observed systems on which it was nearly impossible to log in via SSH 
> > > because of this, and I could reproduce the problem locally to create a 
> > > local DoS where a single user could prevent anybody from logging in.  
> > > 2.6.15 has improved a lot on this (pauses have reduced from 35 seconds 
> > > to 4 seconds) but it's still not very good.
> 
> Hi Willy,
> 
> BTW, if you try my stuff, it'd be good to try just the "cleanup" patch
> first.  It seems very likely to me that your problem is mostly caused by
> the sleep_avg multiplier.  If the first patch cures your woes, try
> killing just the multiplier in virgin source.

Hi again Willy,

Well.  I've done some testing with apache, and I can reproduce the
problem... too darn well in fact.  It's really bad in 2.6.15 here as
well, and while removing the sleep_avg multiplier and the requeue in
schedule() improved things quite a bit, I still have nasty 30s delays
while trying to pipe commands.  These things alone apparently aren't
going to be enough if you want to ssh into a busy server.

	-Mike

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/