netdev - Re: Loopback performance from kernel 2.6.12 to 2.6.37

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Date:	Tue, 09 Nov 2010 15:25:42 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <jdb@...x.dk>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: Loopback performance from kernel 2.6.12 to 2.6.37

Le mardi 09 novembre 2010 à 15:16 +0100, Jesper Dangaard Brouer a
écrit :
> On Tue, 2010-11-09 at 14:59 +0100, Jesper Dangaard Brouer wrote:
> > On Mon, 2010-11-08 at 16:06 +0100, Eric Dumazet wrote:
> > ...
> > > > > > > I noticed that the loopback performance has gotten quite bad:
> > > > > > > 
> > > > > > > http://www.phoronix.com/scan.php?page=article&item=linux_2612_2637&num=6
> 
> > > Their network test is basically :
> > > 
> > > netcat -l 9999 >/dev/null &
> > > time dd if=/dev/zero bs=1M count=10000 | netcat  127.0.0.1 9999
> > 
> > Should it not be:
> >  netcat -l -p 9999 >/dev/null &
> > 
> > When I run the commands "dd | netcat", netcat never finish/exits, I have
> > to press Ctrl-C to stop it.  What am I doing wrong? Any tricks?
> 
> To fix this I added "-q 0" to netcat.  Thus my working commands are:
> 
>  netcat -l -p 9999 >/dev/null &
>  time dd if=/dev/zero bs=1M count=10000 | netcat -q0 127.0.0.1 9999
> 
> Running this on my "big" 10G testlab system, Dual Xeon 5550 2.67GHz,
> kernel version 2.6.32-5-amd64 (which I usually don't use)
> The results are 7.487 sec:
> 
> time dd if=/dev/zero bs=1M count=10000 | netcat -q0 127.0.0.1 9999
> 10000+0 records in
> 10000+0 records out
> 10485760000 bytes (10 GB) copied, 7,48562 s, 1,4 GB/s
> 
> real    0m7.487s
> user    0m0.224s
> sys     0m9.785s

So far, so good. These are the expected numbers. Now we have to
understand why corei7 gets 38 seconds instead of 8 :)



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