netdev - Re: lots of cpu time spent in skb_copy_bits() in net-next with small mtu

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Date:	Fri, 12 Jun 2009 22:57:41 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Benjamin LaHaise <ben.lahaise@...erion.com>,
	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: lots of cpu time spent in skb_copy_bits() in net-next with small
 mtu

On Fri, 12 Jun 2009, Benjamin LaHaise wrote:

> Just a heads up: something in net-next is resulting in lots of cpu time 
> being spent in skb_copy_bits() (called from tcp_collapse()) when an ethernet 
> interface mtu is lowered to 576 on the source and dest machines running 
> netperf.  This behaviour does not appear in 2.6.29.  I'll try to bisect 
> it this weekend.

I'd suggest somebody goes through DaveM's abstraction patch 915219441d56 
(I'm totally out of time so somebody else has to do it if a timely 
solution is desired)... It was quite messy on those parts and I already 
found one issue from it (2df9001edc3) and wouldn't be too surprised if 
there would be some more lurking around... 

-- 
 i.
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