Re: [Xen-devel] n/w performance degradation

[Nivedita Singhvi <niv@xxxxxxxxxx>]

Ian Pratt wrote:

>  > > What are your memory allocations? How much of a bump do you 
>
> > get if you 
> >
> > > increase memory?
> > Currently, both dom0 and the vm have 128MB. I rebooted with 
> > dom0 having 512MB and VM with 256 MB. Here are the numbers:
> > dom0:
> > [  5]  0.0-10.0 sec    987 MBytes    828 Mbits/sec
> >
> > VM:
> > [  5]  0.0-10.0 sec    938 MBytes    787 Mbits/sec
> >
> > So getting slightly better. I haven't run these with SEDF 
> > though, above are using BVT.
>
> Ah, I expect I know what's going on here.
>
> Linux sizes the default socket buffer size based on how much 'system'
> memory it has.
>
> With a 128MB domU it probably defaults to just 64K. For 256MB it
> probably steps up to 128KB. You can prove this by setting
> /proc/sys/net/core/{r,w}mem_{max,default}.
For TCP sockets, you'll also have to bump up
net/ipv4/tcp_rmem[1,2] and net/ipv4/tcp_wmem[1,2],
don't forget.

Fow low mem systems, the default size of the tcp read buffer
(tcp_rmem[1]) is 43689, and max size (tcp_rmem[2]) is
2*43689, which is really too low to do network heavy
lifting.

> For a gigabit network you need at least 128KB.
>
> Ian
At least.

thanks,
Nivedita





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