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

[Nivedita Singhvi <niv@xxxxxxxxxx>]

Artur Schiefer wrote:
> 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
I would highly recommend also increasing the default
size that the buffer is. The TCP buffer increase relies
on learning from the behaviour of the traffic - but
a large number of connections do not last very long.
If you have a moderate sized or smallish file to send,
you don't catch up fast enough.

Try:

net.ipv4.tcp_rmem = 1398080
net.ipv4.tcp_wmem = 1398080

thanks,
Nivedita

> 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.
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
>
>
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