[Mpi3-rma] draft of a proposal for RMA interfaces

[Howard Pritchard]

Hello Folks,

Try again with the correction:

original -

the GET transfers from the caller memory(origin) to the target memory;
PUT transfer data from the target memory to the caller memory

what was probably meant -

the PUT transfers from the caller memory(origin) to the target memory;
  GET transfer data from the target memory to the caller memory

Sorry about that,

Howard

Howard Pritchard wrote:

> Hello Rich,
>
> I meant to respond earlier to Vinod's proposal, sorry for the delay.
>
> First a minor correction in section 5.1. I think the prhase:
>
> /the GET transfers from the caller memory(origin) to the target memory;
> PUT transfer data from the target memory to the caller memory/
>
> near the beginning of section.
>
> I think overall the proposal looks interesting. I am somewhat confused
> by the MPI_Req_set_attr and MPI_Req_get_attr and how they are suppose
> to be used.
>
> The main item that is missing seems to be a method for signaling 
> completion
> of an rma operation at a remote process. Is the assumption that if 
> this was required,
> the remote process would spin wait on a volatile? This would seem to 
> introduce
> other problems - like how to 'emulate' this functionality using 
> point-to-point
> protocols. I believe that any new rma proposal needs to have semantics 
> such that
> one could base a correct, if low performance, implementation using 
> point-to-point
> communication protocols.
>
> Howard
>
> Richard Graham wrote:
>
>> Just to get discussion going again. Talking with several folks I have 
>> heard several concerns expressed about the proposal. I think it would 
>> be good if these (and others) could be raised on the list, so we can 
>> start discussion. We can continue this next week in Chicago, but 
>> Vinod will not be able to make this meeting, so an e-mail discussion 
>> will help.
>>
>> Here are the issues I have hear of so far:
>> - May not work well on current h/w that is not cache coherent, as it 
>> requires a remote thread in this case. I believe this is for the SX 
>> series of machines, but Jesper please correct me if I am wrong here. 
>> What would be an alternative approach that could provide expected 
>> performance on platforms that may require work on the remote end for 
>> RMA for correctness, and work well on platforms that do require very 
>> specific remote cache management (or other actions) for correctness ?
>> - Concern about future high-end platforms, under that assumption that 
>> these will not be cache coherent (and will actually have caches – if 
>> they don’t this is not a concern), and therefore this proposal is 
>> aimed at a short-lived technical capability.
>> - What is missing ?
>>
>> Rich
>>
>>
>> On 9/6/08 6:06 PM, "Vinod tipparaju" <tipparajuv at hotmail.com> wrote:
>>
>>
>>
>>     Rajeev,
>>
>>     Excellent questions.
>>
>>     Technically, yes. However, ARMCI does more thinking about Global
>>     Arrays. Particularly because of stride data transfers (multiple
>>     stride levels). However, I don't see why we cannot have an
>>     alternative port. The only way to know is to prototype the
>>     interfaces, implement Global Arrays on top of them and see how the
>>     interfaces fare. From superficial thinking, I think they will do
>>     just fine ;-). We however cannot say this about all potential
>>     implementations.
>>
>>     I am not sure if Dan Bonachea is a member of this list. I will
>>     write him a message if he isn't.
>>
>>     Thanks,
>>     Vinod.
>>
>>     ----------------------------------------
>>
>>> From: thakur at mcs.anl.gov
>>> To: mpi3-rma at lists.mpi-forum.org
>>> Date: Sat, 6 Sep 2008 16:24:35 -0500
>>> Subject: Re: [Mpi3-rma] draft of a proposal for RMA interfaces
>>>
>>> Vinod,
>>> Thanks for the proposal and the nice presentation. A question I had
>>> was does it meet the needs of the Global Arrays library? That is,
>>
>>     if this
>>
>>> were available in MPI today, would you implement Global Arrays
>>
>>     with MPI and
>>
>>> nothing else (not ARMCI). Similarly, it would be good to run it
>>
>>     by Dan
>>
>>> Bonachea and see what he has to say regarding implementing UPC.
>>>
>>> Regards,
>>> Rajeev
>>>
>>>
>>>> -----Original Message-----
>>>> From: mpi3-rma-bounces at lists.mpi-forum.org
>>>> [mailto:mpi3-rma-bounces at lists.mpi-forum.org] On Behalf Of
>>>> Vinod tipparaju
>>>> Sent: Thursday, September 04, 2008 1:50 AM
>>>> To: mpi3-rma at lists.mpi-forum.org
>>>> Subject: [Mpi3-rma] draft of a proposal for RMA interfaces
>>>>
>>>>
>>>> Folks,
>>>>
>>>> Attached is a draft of a new proposal for MPI3-RMA interfaces
>>>> for your perusal.
>>>>
>>>> Thanks,
>>>> Vinod Tipparaju, ORNL.
>>>>
>>>
>>> _______________________________________________
>>> mpi3-rma mailing list
>>> mpi3-rma at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>
>>
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>>
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>>
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>>  
>>
>
>


-- 

Howard Pritchard 
Cray Inc.