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Subject: Re: [OMPI devel] iprobe and opal_progress
From: Terry Dontje (Terry.Dontje_at_[hidden])
Date: 2008-06-18 10:25:59


Ok, I'll see if I can figure out the below. Though is this really
something that can be used in both MPI_Iprobe and MPI_Probe? One other
question, is the use of opal_progress in MPI_Iprobe the right thing to
do? Is there something a little lighter weight (bml_progress maybe)?

--td

George Bosilca wrote:
> I kind of remember that we had a discussion about this long ago, and
> that we decided to have it this way for latency. Now looking at the
> code it seems way to ugly to me. I think Brian have a point. MPIPobe
> and MPI_Iprobe are MPI functions, and they are expected to make
> progress all the time. So call opal_progress, then do the probe seems
> like the smartest and simplest approach.
>
> However, if you want to do this, then it's better if we do it in the
> right way. What we have today in the PML OB1 or probe is horribly
> expensive. Initialize a complete request, that will never be used for
> anything than matching is an overkill. The only fields that you really
> need are the flags and the matching information. How about, creating a
> request, setting these flags and then call the matching directly ?
> This way, we can create a special path or probes, and this will remove
> some ifs from the critical path for receives ...
>
> george.
>
> On Jun 18, 2008, at 3:57 PM, Brian W. Barrett wrote:
>
>> On Wed, 18 Jun 2008, Terry Dontje wrote:
>>
>>> Jeff Squyres wrote:
>>>> Perhaps we did that as a latency optimization...?
>>>> George / Brian / Galen -- do you guys know/remember why this was done?
>>>> On the surface, it looks like it would be ok to call progress and
>>>> check again to see if it found the match. Can anyone think of a
>>>> deeper reason not to?
>>> If it is ok to check again, my next question is going to be how?
>>> Because after looking at the code some more I found iprobe requests
>>> are not actually queued. So can I just do another
>>> MCA_PML_OB1_RECV_REQUEST_START on the init'd IPROBE_REQUEST after
>>> the call opal_progress to force a search on the unexpected queue or
>>> do I need to FINI the request and regenerate it again?
>>
>> I think you'd have to re-init the request at a minimum. In other
>> words, just always call opal_progres at the top of iprobe and be done
>> :).
>>
>> Brian
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