[mvapich-discuss] MV2_USE_BLOCKING=1 with ch3:psm

[David Winslow]

Thanks Adam for the response.

In your experience, what is the reduction in latency using verbs instead of
PSM?

David





On Thu, Aug 21, 2014 at 2:59 PM, Adam T. Moody <moody20 at llnl.gov> wrote:

> Hi David and Leonard,
> We have many QLogic clusters at LLNL.
>
> The problem lies with Intel's PSM library itself.  PSM does not provide a
> notification mechanism to wake MPI when a message comes in, so MPI's only
> option is to poll.  Right now, MVAPICH repeatedly calls psm_mq_ipeek() to
> test for a received message.
>
> The best you can do right now is to yeild the CPU on occassion from within
> MPI.  However, this just releases the CPU if another process is ready to
> run, so your CPU still churns at 100%.
>
> If you value blocking behavior more than bandwidth and latency, one
> solution may be to configure MVAPICH to use verbs instead of PSM.
> -Adam
>
>
> David Winslow wrote:
>
>  Leonard,
>> I have the same issue. Hari suggested MV2_ON_DEMAND_THRESHOLD=1 but it
>> didn't work for me. CPU usage still at 100% when just waiting. You could
>> try this and see if it works for you. Let me know if it does.
>>
>> Thanks,
>> David
>>
>>
>> On Thu, Aug 21, 2014 at 11:29 AM, Leonardo Piga <leonardo.piga at gmail.com>
>> wrote:
>>
>>
>>
>>> Hi all,
>>>
>>> I am a new user of MVAPICH2.
>>>
>>> I am trying to run mvapich2-2.0 using MV2_USE_BLOCKING=1. However, the
>>> CPU usage is still high during wait (I tested for MPI_Allreduce).
>>>
>>> I don't want to keep CPU usage high when a process is waiting. Is
>>> there a way to do this with CH3 PSM?
>>>
>>> Thank you.
>>> --
>>> Leonardo
>>> _______________________________________________
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>>> mvapich-discuss at cse.ohio-state.edu
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>>>
>>>
>>>
>>
>>
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