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

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

 > > 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 a gigabit network you need at least 128KB.

Ian

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