[mpiwg-hybridpm] Hybrid/Accelerator WG Meeting

Jim Dinan james.dinan at gmail.com
Thu Mar 11 09:07:44 CST 2021

Unfortunately, CPU callbacks are not a perfect solution on their own. CUDA
does not allow CUDA calls from within CPU callbacks, so for example you
would not be able to launch data packing kernels or peer-to-peer copy
operations from within the callback. However, you can use CPU callbacks to
signal a thread in the MPI runtime to process the operation. Another option
in this design space is to use CUDA memops (e.g. cuStreamWriteValue64 or
cuStreamWaitValue64) to coordinate between CUDA streams and MPI
communication helper threads. Because memops are processed from within the
GPU control processor that manages stream execution, I would expect these
to have lower overheads than CPU callbacks (although I haven't measured


On Wed, Mar 10, 2021 at 10:08 PM Junchao Zhang <junchao.zhang at gmail.com>

> Jim,
>   Thanks for the slides.  In Stephen's presentation today, it seems
> with existing techniques, i.e, CPU MPI callback nodes in CUDA graphs, one
> can solve the MPI GPU problem. Is my understanding correct?
>   Thanks.
> --Junchao Zhang
> On Wed, Mar 10, 2021 at 8:34 PM Jim Dinan via mpiwg-hybridpm <
> mpiwg-hybridpm at lists.mpi-forum.org> wrote:
>> Hi All,
>> I've posted Stephen's slides:
>> https://github.com/mpiwg-hybrid/hybrid-issues/tree/master/slides
>> Best,
>>  ~Jim.
>> On Mon, Mar 8, 2021 at 11:21 AM Jim Dinan <james.dinan at gmail.com> wrote:
>>> Hi All,
>>> We have an invited speaker this week at the HACC WG:
>>> Topic: CUDA Deep Dive For the MPI Forum HACC WG
>>> When:  Wednesday, March 10 10-11:00am ET
>>> Connection Info: https://github.com/mpiwg-hybrid/hybrid-issues/wiki
>>> Speaker: Stephen Jones, NVIDIA
>>> Stephen Jones is one of the architects of CUDA, working on defining the
>>> language, the platform, and the hardware that it runs on, to span the needs
>>> of parallel programming from high performance computing to artificial
>>> intelligence. Prior to his present position, he lead the Simulation &
>>> Analytics group at SpaceX, working on large-scale simulation of rocket
>>> engines. He has worked in diverse other industries, including networking,
>>> CAD/CAM, and scientific computing. He has been a part of CUDA since 2008.
>>> Cheers,
>>>  ~Jim.
>>> PS - Apologies for cross posting on the main list. If you would like to
>>> continue receiving emails relating to the Hybrid & Accelerator WG, please
>>> sign up for the mailing list here:
>>> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-hybridpm.
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