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MPI_Waitsome performance improvement (version #2) #1821

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merged 1 commit into from
Sep 8, 2016
Merged

MPI_Waitsome performance improvement (version #2) #1821

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28 changes: 18 additions & 10 deletions ompi/request/req_wait.c
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Original file line number Diff line number Diff line change
Expand Up @@ -391,8 +391,8 @@ int ompi_request_default_wait_some(size_t count,
num_requests_null_inactive++;
continue;
}

if( !OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, REQUEST_PENDING, &sync) ) {
indices[i] = OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, REQUEST_PENDING, &sync);
if( !indices[i] ) {
/* If the request is completed go ahead and mark it as such */
assert( REQUEST_COMPLETE(request) );
num_requests_done++;
Expand Down Expand Up @@ -423,15 +423,23 @@ int ompi_request_default_wait_some(size_t count,
if( request->req_state == OMPI_REQUEST_INACTIVE ) {
continue;
}
/* Atomically mark the request as pending. If this succeed
* then the request was not completed, and it is now marked as
* pending. Otherwise, the request is complete )either it was
* before or it has been meanwhile). The major drawback here
* is that we will do all the atomics operations in all cases.
/* Here we have 3 possibilities:
* a) request was found completed in the first loop
* => ( indices[i] == 0 )
* b) request was completed between first loop and this check
* => ( indices[i] == 1 ) and we can NOT atomically mark the
* request as pending.
* c) request wasn't finished yet
* => ( indices[i] == 1 ) and we CAN atomically mark the
* request as pending.
* NOTE that in any case (i >= num_requests_done) as latter grows
* either slowly (in case of partial completion)
* OR in parallel with `i` (in case of full set completion)
*/
if( !OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, &sync, REQUEST_PENDING) ) {
indices[num_requests_done] = i;
num_requests_done++;
if( !indices[i] ){
indices[num_requests_done++] = i;
} else if( !OPAL_ATOMIC_CMPSET_PTR(&request->req_complete, &sync, REQUEST_PENDING) ) {
indices[num_requests_done++] = i;
}
}
sync_unsets = count - num_requests_null_inactive - num_requests_done;
Expand Down