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From: Terry D. Dontje (Terry.Dontje_at_[hidden])
Date: 2007-08-13 07:16:41


Jeff Squyres wrote:

>With Mellanox's new HCA (ConnectX), extremely low latencies are
>possible for short messages between two MPI processes. Currently,
>OMPI's latency is around 1.9us while all other MPI's (HP MPI, Intel
>MPI, MVAPICH[2], etc.) are around 1.4us. A big reason for this
>difference is that, at least with MVAPICH[2], they are doing wire
>protocol header caching where the openib BTL does not. Specifically:
>
>- Mellanox tested MVAPICH with the header caching; latency was around
>1.4us
>- Mellanox tested MVAPICH without the header caching; latency was
>around 1.9us
>
>Given that OMPI is the lone outlier around 1.9us, I think we have no
>choice except to implement the header caching and/or examine our
>header to see if we can shrink it. Mellanox has volunteered to
>implement header caching in the openib btl.
>
>Any objections? We can discuss what approaches we want to take
>(there's going to be some complications because of the PML driver,
>etc.); perhaps in the Tuesday Mellanox teleconf...?
>
>
This sounds great. Sun, would like to hear how thing are being done
so we can possibly port the solution to the udapl btl.

--td