[mpich-discuss] Question about non-blocking MPI - 3

[Joachim Protze]

Hi Viet,

If MPICH_ASYNC_PROGRESS=1 is necessary for your application to
terminate, i.e., you see a deadlock without this flag, the applications
has a correctness/portability issue. This env variable should only have
a possible impact to performance (better compute/communication overlap)
but should not be necessary to avoid deadlock.

You can compare this to the classical send-send deadlock (example 3.9 in
the standard), where the application relies on buffering / eager
communication, but all send suddenly block. The portable fix for the
application is not to increase the eager-limit, but to fix the
communication pattern.

Best
Joachim

Am 07.01.21 um 13:08 schrieb viet via discuss:
> Dear Hui Zhou,
> 
> Thank you for your response to this thread.
> Could you give me some references on this issue?
> 
> It seems that the below environment setting is necessary.
> 
> MPICH_ASYNC_PROGRESS=1
> 
> Thank you for anything you can provide.
> Best, Viet.
> 
> 
> 
> On Tue, Jan 5, 2021 at 5:59 AM Zhou, Hui <zhouh at anl.gov> wrote:
> 
>> You don’t need any special settings to use non-blocking MPI collectives in
>> MPICH.
>>
>>
>>
>> --
>> Hui Zhou
>>
>>
>>
>>
>>
>> *From: *viet via discuss <discuss at mpich.org>
>> *Date: *Friday, December 4, 2020 at 7:12 AM
>> *To: *discuss at mpich.org <discuss at mpich.org>
>> *Cc: *teivml at gmail.com <teivml at gmail.com>
>> *Subject: *[mpich-discuss] Question about non-blocking MPI - 3
>>
>> Hello everyone,
>>
>> What is the environment setting for the use of non-blocking MPI-3 *
>> collectives in mpich3.3?
>>
>> In Intel MPI, the setting is as follows
>>
>> $ export I_MPI_ASYNC_PROGRESS=1
>> $ export I_MPI_ASYNC_PROGRESS_PIN=<CPU list>
>>
>> Is there an equivalent setting in mpich3.3?
>> Thank you,
>> Viet.
>>
> 
> 
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-- 
Dipl.-Inf. Joachim Protze

IT Center
Group: High Performance Computing
Division: Computational Science and Engineering
RWTH Aachen University
Seffenter Weg 23
D 52074  Aachen (Germany)
Tel: +49 241 80- 24765
Fax: +49 241 80-624765
protze at itc.rwth-aachen.de
www.itc.rwth-aachen.de

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