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Subject: Re: [OMPI devel] algorithm selection in open mpi
From: Pavel Mezentsev (pavel.mezentsev_at_[hidden])
Date: 2012-04-03 09:01:15


Is there a way to specify collective depending on the size of the message
and number of processes?

Regards,
Pavel Mezentsev

2012/4/3 George Bosilca <bosilca_at_[hidden]>

> Roswan,
>
> There a re simpler solutions to achieve this. We have a built-in mechanism
> to select a specific collective implementation. Here is what you have to
> add in your .openmpi/mca-params.conf (or as MCA argument on the command
> line):
>
> coll_tuned_use_dynamic_rules = 1
> coll_tuned_bcast_algorithm = 6
>
> The first one activate the dynamic selection of collective algorithms,
> while the second one force all broadcast to be of the type 6 (binomial
> tree). Btw, once you set the first one, do a quick "ompi_info --param coll
> tuned" to see the list of all possible options for the collective algorithm
> selection.
>
> george.
>
> On Apr 2, 2012, at 23:10 , roswan ismail wrote:
>
> Hi all..
>
> I am Roswan Ismail from Malaysia. I am focusing on MPI communication
> performance on quad-core cluster at my university. I used Open MPI-1.4.3
> and measurements were done using scampi benchmark.
>
> As I know, open MPI used multiple algorithms to broadcast data (MPI_BCAST)
> such as binomial, pipeline, binary tree, basic linear and split binary
> tree. All these algorithms will be used based on message size and
> communicator size. For example, binomial is used when message size to be
> broadcasted is small while pipeline used for broadcasting a large message.
>
> What I want to do now is, to use fixed algorithm i.e binomial for all
> message size. I want to see and compare the results with the default
> results. So, I was modified coll_tuned_decision_fixed.c which is located in
> open mpi-1.4.3/ompi/mca/coll/tuned by returning binomial algorithm for all
> condition. Then I recompile the files but the problem is, the results
> obtained is same as default. It seems I do not do any changes to the codes.
>
> So could you guys tell me the right way to do that.
>
> Many thanks
>
> **
> *Roswan Binti Ismail,
> FTMK,
> Univ. Pend. Sultan Idris,
> Tg Malim, Perak.
> Pej: 05-4505173
> H/P: 0123588047
> iewanis_at_[hidden] <iewanis1402_at_hotmail>
> roswan_at_[hidden]
> ***
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