netdev - Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32

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Message-ID: <1317757118.3580.24.camel@Joe-Laptop>
Date:	Tue, 04 Oct 2011 12:38:38 -0700
From:	Joe Perches <joe@...ches.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	starlight@...nacle.cx, Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Willy Tarreau <w@....eu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephen Hemminger <stephen.hemminger@...tta.com>
Subject: Re: big picture UDP/IP performance question re 2.6.18  -> 2.6.32

On Tue, 2011-10-04 at 14:16 -0500, Christoph Lameter wrote:
> On Mon, 3 Oct 2011, starlight@...nacle.cx wrote:
> > I've come to the conclusion that Eric is right
> > and the primary issue is an increase in the
> > cost of scheduler context switches.  Have
> > been watching this number and it has held
> > pretty close to 200k/sec under all scenarios
> > and kernel versions, so it has to be
> > a longer code-path, bigger cache pressure
> > or both in the scheduler.  Sadly this makes
> > newer kernels a no-go for us.
> We had similar experiences. Basically latency constantly gets screwed up
> by the new fancy features being added to the scheduler and network
> subsystem (most notorious is the new "fair" scheduler, 2.6.23 made a big
> step down).

Idly curious, have you compared bfs performance?
http://ck.kolivas.org/patches/bfs/bfs-faq.txt


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