netdev - Re: tun: performance regression in 2.6.30-rc1

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Message-ID: <20090416235100.GD29988@gondor.apana.org.au>
Date:	Fri, 17 Apr 2009 07:51:00 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <m.s.tsirkin@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: tun: performance regression in 2.6.30-rc1

On Fri, Apr 17, 2009 at 12:31:22AM +0300, Michael S. Tsirkin wrote:
> Hi,
> I have a simple test that sends 10K packets out of a tap device.  Average time
> needed to send a packet has gone up from 2.6.29 to 2.6.30-rc1.
> 
> 2.6.30-rc1:
> 
> #sh runsend
> time per packet:       7570 ns
> 
> 2.6.29:
> 
> #git checkout v2.6.29 -- drivers/net/tun.c
> #make modules modules_install
> #rmmod tun
> #sh runsend
> time per packet:       6337 ns
> 
> I note that before 2.6.29, all tun skbs would typically be linear,
> while in 2.6.30-rc1, skbs for packet size > 1 page would be paged.
> And I found this comment by Rusty (it appears in the comment for
> commit f42157cb568c1eb02eca7df4da67553a9edae24a):

Again this should already be fixed in the latest net-2.6.

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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