Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: Re: [OMPI users] scaling problem with openmpi
From: Pavel Shamis (Pasha) (pashash_at_[hidden])
Date: 2009-05-21 03:09:46


> I tried to run with the first dynamic rules file that Pavel proposed
> and it works, the time per one MD step on 48 cores decreased from 2.8
> s to 1.8 s as expected.
>
Good news :-)

Pasha.
> Thanks
>
> Roman
>
> On Wed, May 20, 2009 at 7:18 PM, Pavel Shamis (Pasha) <pashash_at_[hidden]> wrote:
>
>> Tomorrow I will add some printf to collective code and check what really
>> happens there...
>>
>> Pasha
>>
>> Peter Kjellstrom wrote:
>>
>>> On Wednesday 20 May 2009, Pavel Shamis (Pasha) wrote:
>>>
>>>
>>>>> Disabling basic_linear seems like a good idea but your config file sets
>>>>> the cut-off at 128 Bytes for 64-ranks (the field you set to 8192 seems
>>>>> to
>>>>> result in a message size of that value divided by the number of ranks).
>>>>>
>>>>> In my testing bruck seems to win clearly (at least for 64 ranks on my
>>>>> IB)
>>>>> up to 2048. Hence, the following line may be better:
>>>>>
>>>>> 131072 2 0 0 # switch to pair wise for size 128K/nranks
>>>>>
>>>>> Disclaimer: I guess this could differ quite a bit for nranks!=64 and
>>>>> different btls.
>>>>>
>>>>>
>>>> Sounds strange for me. From the code is looks that we take the threshold
>>>> as
>>>> is without dividing by number of ranks.
>>>>
>>>>
>>> Interesting, I may have had to little or too much coffe but the figures in
>>> my previous e-mail (3rd run, bruckto2k_pair) was run with the above line.
>>> And it very much looks like it switched at 128K/64=2K, not at 128K (which
>>> would have been above my largest size of 3000 and as such equiv. to
>>> all_bruck).
>>>
>>> I also ran tests with:
>>> 8192 2 0 0 # ...
>>> And it seemed to switch between 10 Bytes and 500 Bytes (most likely then
>>> at 8192/64=128).
>>>
>>> My testprogram calls MPI_Alltoall like this:
>>> time1 = MPI_Wtime();
>>> for (i = 0; i < repetitions; i++) {
>>> MPI_Alltoall(sbuf, message_size, MPI_CHAR,
>>> rbuf, message_size, MPI_CHAR, MPI_COMM_WORLD);
>>> }
>>> time2 = MPI_Wtime();
>>>
>>> /Peter
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> users mailing list
>>> users_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>>
>
>