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

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Date:	Sat, 01 Oct 2011 21:11:43 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	starlight@...nacle.cx
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32

Le samedi 01 octobre 2011 à 14:16 -0400, starlight@...nacle.cx a écrit :
> At 08:44 AM 10/1/2011 +0200, Eric Dumazet wrote:
> >In my experience, I have the exact opposite :
> >performance greatly improved in recent
> >kernels. Unless you compile your kernel to include
> >new features that might reduce performance
> >(namespaces, cgroup, ...)
> 
> RH has both of the above turned on in the
> 2.6.32-71.29.1.el6.x86_64 kernel tested.
> 
> If these are big negatives to network
> performance, could you list what should
> specifically turned off to maximize
> results?  Also a recommendation for
> the best recent kernel for another
> benchmark would be helpful.
> 
> Probably can't convince anyone to deploy a
> kernel without commercial support, but if
> an alternate compile fixes performance it
> might be possible to convince RH to support
> the alternative build.
> 

2.6.32 has a perf tool, that can really help to spot in a few minutes
hot spots. That would definitely help to further diagnose what could be
the problem in your workload.

A single patch can have huge performance impact, sometime not noticed.

For example, in 2.6.36, AF_UNIX support for pid namespaces dropped
performance a lot [commit 7361c36c5224 (af_unix: Allow credentials to
work across user and pid namespaces)], because of a single atomic
operation, but done on each send() and receive() on a central location.



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