Re: n/w performance degradation

[Nivedita Singhvi <niv@us.ibm.com>]

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