Re: Loopback performance from kernel 2.6.12 to 2.6.37

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mardi 09 novembre 2010 à 14:59 +0100, Jesper Dangaard Brouer a
écrit :
> 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
> > >
> 
> > CC netdev, if you dont mind.
> 
> No problem :-)
> 
> > 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 &
> 

It depends on netcat version. On yours, yes, you need the "-p"

> 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?
> 
> "dd" reports 17.54 sec, and but the "time" measurement cannot be uses as
> the netcat just hangs/waits for more data...
> 

Your netcat version needs a "-c" switch

time dd if=/dev/zero bs=1M count=10000 | netcat -c 127.0.0.1 9999


> time dd if=/dev/zero bs=1M count=10000 | netcat 127.0.0.1 9999
> 10000+0 records in
> 10000+0 records out
> 10485760000 bytes (10 GB) copied, 17,5419 s, 598 MB/s
> 
> When I run the commands, I see 261682 context switches per sec...
> 
> This quick test were on a Core i7 920 using kernel
> 2.6.32-rc3-net-next-dev-mp2t.
> 

32 or 64bit kernel ?

Thanks !