netdev - Re: High contention on the sk_buff

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Message-ID: <49C16349.9030503@us.ibm.com>
Date:	Wed, 18 Mar 2009 14:10:33 -0700
From:	Vernon Mauery <vernux@...ibm.com>
To:	David Miller <davem@...emloft.net>
CC:	andi@...stfloor.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: High contention on the sk_buff_head.lock

David Miller wrote:
> From: Andi Kleen <andi@...stfloor.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.

--Vernon
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