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

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Date:	Tue, 04 Oct 2011 15:45:21 -0400
From:	starlight@...nacle.cx
To:	Joe Perches <joe@...ches.com>, Christoph Lameter <cl@...two.org>
Cc:	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

At 12:38 PM 10/4/2011 -0700, Joe Perches wrote:
>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

No but it certainly does look very interesting.

Looks like trying it out not much more work than
patching and building a kernel and running the
benchmark.  Will take a look and report back
if I do.  Little busy at present but should
have time in a week or so.

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