Re: [Re: [Xen-users] Slow domU network

[Artur Schiefer <aschiefer@xxxxxx>]

hello,

somehow the linux network core tries to adjust itself to its
environment. as i recently learned theese parameters are optimized for
100 mbit networking. from another poster i got the info that you have to
set the following parameters in your "/etc/sysctl.conf" to achieve gbit
speed:
# increase TCP maximum buffer size
net.core.rmem_max=16777216
net.core.wmem_max=16777216

# increase Linux autotuning TCP buffer limits
# min, default, and maximum number of bytes to use
net.ipv4.tcp_rmem=4096 87380 16777216
net.ipv4.tcp_wmem=4096 65536 16777216

BUT THIS ONLY SOLVES THE PROBLEM FOR WITHIN DOMU COMMUNCATION (i.e.
sender and receiver are the SAME virtual maschine, which should be a
theoretical problem in most cases). I tuned domU and dom0 this way
problem between dom0 and domU still exists. i also played with tcp
window sizes (-w option in iperf) from 64kb to 2MB but the performance
differences are negligable.


Am Donnerstag, den 09.03.2006, 20:38 +0200 schrieb Pasi Kärkkäinen:
> On Thu, Mar 09, 2006 at 05:26:03PM +0100, Artur Schiefer wrote:
> > ok, solved the problem for within domu communcation, was an autotuning
> > effect.
> > 
> 
> Autotuning effect? Please be more specific because many of the xen users
> seem to have problems with network performance..
> 
> -- Pasi
>        
>                                    ^
>                                 .     .
>                                  Linux
>                               /    -    \
>                              Choice.of.the
>                            .Next.Generation.
> 
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