[ofa-general] Terrible TCP Qperf Performance with Centos 5.2 and default settings

[Tziporet Koren]

Robert Dunkley wrote:
>
> I see very low qperf TCP performance of IPOIB on Centos 5.2 by default 
> (RDMA performance is fine).
>
Can you use netpef for IPoIB testing - this will be able to compare to 
measurements we take here
>
> Centos sets the maximum MTU for ib0 on boot automatically. For CM 
> centos sets the maximum MTU that is just slightly less than the 
> logical 65536 setting. Connected mode only seems to like nice round 
> MTU values (eg. 32768 or 2048) so the default setting always gives 
> terrible performance.
>
In OFED 1.3.1 we have a problem when moving from UD to CM in setting of 
the MTU of CM mode to the maximum allowable value.
To workaround this feature, the user requires to do the following 
actions to ensure the MTU setting is done correctly:
 
1. ifconfig ib0
2. Take note of the MTU specified, let's call it xmtu. Let's call ymtu = 
xmtu - 10
3. ifconfig ib0 mtu ymtu
4. ifconfig ib0 mtu xmtu
 
The above procedure is valid for any ib<x> interface.

Tziporet