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Subject: Re: [OMPI devel] MPI_Request_get_status and opal_progress [PATCH]
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-09-17 10:12:19


On Sep 14, 2009, at 5:12 PM, Shaun Jackman wrote:

> Two questions. Should the loop label recheck_request_status come
> before or after the call to opal_atomic_mb?
>

I believe that a 2nd mb is necessary. But I think it could be put
into the "if" block at the end, and leave the label where it is. But
see below.

> Is it necessary to check
> request->req_state a second time, or is it only necessary to check
> request->req_complete the second time?
>

In THREAD_MULTIPLE, I guess the state could change. But in non-
THREAD_MULTIPLE, it's superfluous to check a 2nd time because a
request can't have changed into INACTIVE simply due to a call to
opal_progress(). I notice that req_test.c checks the whole enchilada
again (including the mb and state change). Since we're currently not
distinguishing between THREAD_MULTIPLE and not in these functions, I
think we need to be conservative and check the state again.

I think this means that our TEST/WAIT functions are not well-tuned for
threading (or, at least, there are optimizations that could be made
based on the thread level).

George / Brian -- got opinions here?

-- 
Jeff Squyres
jsquyres_at_[hidden]