Re: [Xen-devel] MPI benchmark performance gap between native linux anddomU

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 5 Apr 2005, at 03:07, Santos, Jose Renato G (Jose Renato Santos) 
wrote:
>  Here is a brief explanation of the problem we found and the solution
> that worked for us.
>   Xenolinux allocates a full page (4KB) to store socket buffers instead
> of using just MTU bytes as in traditional linux. This is necessary to
> enable page exchanges between the guest and the I/O domains. The side
> effect of this is that memory space used for  socket buffers is not 
> very
> efficient.
This is true, but these days we lie to the network stack about how big 
the skb data area is. The 'truesize' field, which is what I think is 
used for socket buffer accounting, will be around 1600 bytes, not 4096. 
So I would expect the old trick of reducing the receive windows not to 
work: but if it does then that is very interesting!
 -- Keir


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