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SubjectRe: High contention on the sk_buff_head.lock
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From: Vernon Mauery <vernux@us.ibm.com>
Date: Wed, 18 Mar 2009 14:10:33 -0700

> David Miller wrote:
> > From: Andi Kleen <andi@firstfloor.org>
> > Date: Wed, 18 Mar 2009 21:54:37 +0100
> >
> >> But then again I'm not sure it's worth it if the problem only
> >> happens in out of tree RT.
> > The list of problems that only show up with the RT kernel seems to be
> > constantly increasing, but honestly is very surprising to me.
> > I don't understand why we even need to be concerned about this stuff
> > upstream, to be honest.
> > Please reproduce this in the vanilla kernel, then get back to us.
>
> Huh? The numbers that I posted *were* from the vanilla kernel. I ran
> the 2.6.29-rc8 kernel with lock_stat enabled. The lock contention
> happens on the same lock in both vanilla and -rt, it just happens
> to be more pronounced in the -rt kernel because of the double context
> switches that the sleeping spinlock/rt-mutexes introduce.

And the double context switches are probably also why less
natural batching and locality are achieved in the RT kernel.

Isn't that true?


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