[openib-general] [PATCH] osm: PathRecord prefer 1K MTU for MT23108 devices

[Or Gerlitz]

Michael S. Tsirkin wrote:
> Quoting r. Or Gerlitz <ogerlitz at voltaire.com>:

>> Eitan Zahavi wrote:
>>> The following patch solves an issue with OpenSM preferring largest MTU 
>>> for PathRecord/MultiPathRecord for paths going to or from MT23108 (Tavor)
>>> devices instead of using a 1K MTU which is best for this device.

>> Isn't the 2K MTU issue with Tavor comes into play only under RC QP?

> I don't think so, no. Tavor supports 2K MTU, but it has better performance with
> 1K MTU than 2K MTU. QP type should not matter.

Can you double check that please, as far as i know there is something 
like BW 40-50% drop with Tavor/RC/2048 vs Tavor/RC/1024 but the BW with 
Tavor/UD/2048 is **no less** then Tavor/UD/1024.

So its very common for IPoIB net devices impl. to expose 2044 or 1500 
bytes MTU to the OS eg to cope with Ethernet and reduce IP 
fragmentation/reassembly of UDP/TCP traffic.

Or.