On Jul 2, 2007, at 5:15 PM, Galen Shipman wrote:
While I think the SRC design makes sense I also have concerns
regarding SSQ.
As Gleb has pointed out, if the hardware doesn't do the demux then
the application has to. It sounds like there are two proposals to
deal with this hardware limitation in software (sigh).
1) Process A polls CQ, if WQE belongs to Process B, Process A will
drop the WQE in a shared memory region that Process B will poll.
[snip]
2) Process A peeks CQ, if WQE belongs to Process B, it doesn't
process it [snip]
In my opinion the demux belongs in the hardware, otherwise we end
up complicating an already complicated code base to support a
feature which unless I am missing something will have no benefit to
real applications.
I agree. I cannot see how SSQ will be useful in Open MPI -- it makes
the code *much* more complicated and effectively guarantees to add
latency for the common case. I don't see how to explain it better
than Gleb/Galen already did.
If Mellanox wants to implement SSQ for other reasons, fine. But
based on the explanations so far, I don't see us using it in [Open] MPI.
--
Jeff Squyres
Cisco Systems
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