[Mpi3-rma] mpi3-rma post from bradc at cray.com requires approval

Pavan Balaji balaji at mcs.anl.gov
Sat Jun 5 18:59:16 CDT 2010

Thanks for listing these. If we are voting for this, my vote would be to 
have (2) and toss out (1) and (3).

  -- Pavan

On 06/05/2010 02:40 PM, Underwood, Keith D wrote:
> I was only giving an example of how tightly ordering COULD be defined.  Ordering options include:
> 1) Ordering within a given replace:  is the first byte guaranteed to get there before the last?
> 2) Ordering between replaces to a given location:  but, what if two replaces are overlapping?
> 3) Ordering among all replaces to a given node
> Two sided gives you something weird, in that it orders the matching of the message headers and not the end of messages or data within the messages.
> Keith
>> -----Original Message-----
>> From: Pavan Balaji [mailto:balaji at mcs.anl.gov]
>> Sent: Saturday, June 05, 2010 3:30 PM
>> To: Underwood, Keith D
>> Cc: MPI 3.0 Remote Memory Access working group; bradc at cray.com
>> Subject: Re: [Mpi3-rma] mpi3-rma post from bradc at cray.com requires
>> approval
>> I see. My definition of ordering was a little bit different from yours.
>> My definition was -- if I do two accumulates with replace on the same
>> location, I'm guaranteed to have the second value in the location. It
>> didn't have any definition of ordering to two different locations.
>> So, I think we need to come to a consensus first on what the actual
>> definition of ordering is.
>>   -- Pavan
>> On 06/05/2010 02:22 PM, Underwood, Keith D wrote:
>>>>> We would need to think about whether we have to have the whole
>>>>> message ordered or ordered on a per target address basis.
>>>> Atomicity and ordering go hand-in-hand; if there's no atomicity,
>>>> ordering doesn't make sense. Since we have basic datatype atomicity
>> for
>>>> accumulate/get_accumulate, ordering would make sense at that
>>>> granularity
>>>> as well.
>>>> If someone wants to propose full-message atomicity, then we can
>>>> consider
>>>> ordering at that granularity too. But till then, whole message
>> ordering
>>>> is an overkill.
>>> Well, they aren't orthogonal, but they aren't quite that tightly
>> linked.  A user that knew that two messages were not going to overlap
>> might want to use a full message ordering from a single node for
>> completion detection.  E.g. an MPI_Accumulate() with "replace" to one
>> buffer and then an MPI_Accumulate() to another buffer to increment a
>> variable and use the full message ordering to be able to use the latter
>> for completion without the expense of a flush() between the messages.
>> So, it has value and a usage scenario.  I just don't know if we want to
>> go that far or not.
>>> Keith
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji

Pavan Balaji

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