Decrease the latency is the main reason. If we delay the MPI
completion, then we always have to call opal_progress at least once in
order to allow the BTL to trigger the callback. In the current
implementation, we never call opal_progress on small messages, unless
there is some kind of resource starvation.
Thanks,
george.
On Nov 8, 2007, at 11:09 AM, Andrew Friedley wrote:
> Brian Barrett wrote:
>> Personally, I'd rather just not mark MPI completion until a local
>> completion callback from the BTL. But others don't like that idea,
>> so
>> we came up with a way for back pressure from the BTL to say "it's not
>> on the wire yet". This is more complicated than just not marking MPI
>> completion early, but why would we do something that helps real apps
>> at the expense of benchmarks? That would just be silly!
>
> FWIW this issue is also very relevant for the UD BTL, especially with
> some new work I've done in the last week (currently having problems
> with
> send-side completion semantics). I missed it, what was the reasoning
> for not marking MPI completion until a callback from the BTL?
>
> Andrew
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