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starpu-devel - Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems

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Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems


Chronologique Discussions 
  • From: Samuel Thibault <samuel.thibault@inria.fr>
  • To: Hatem Ltaief <hatem.ltaief@kaust.edu.sa>
  • Cc: Kadir Akbudak <kadir.akbudak@kaust.edu.sa>, Aniello Esposito <esposito@cray.com>, "starpu-devel@lists.gforge.inria.fr" <starpu-devel@lists.gforge.inria.fr>, Aleksandr Mikhalev <aleksandr.mikhalev@kaust.edu.sa>, "Sameh M. Abdulah" <sameh.abdulah@kaust.edu.sa>
  • Subject: Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems
  • Date: Thu, 26 Apr 2018 17:08:41 +0200
  • Authentication-results: mail2-smtp-roc.national.inria.fr; spf=None smtp.pra=samuel.thibault@inria.fr; spf=Neutral smtp.mailfrom=samuel.thibault@ens-lyon.org; spf=Pass smtp.helo=postmaster@hera.aquilenet.fr
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Hello,

Hatem Ltaief, le jeu. 26 avril 2018 14:57:42 +0000, a ecrit:
> The profiles indicate that most of the time is being spent into internal
> StarPU
> functions:
> || 42.6% | 79,366.5 | 851.5 | 1.1% | _starpu_get_worker_task
> || 2.2% | 4,111.3 | 114.7 | 2.8% | _starpu_handle_pending_node_data_requests
> || 1.9% | 3,523.9 | 145.1 | 4.1% | _starpu_cpu_worker
> || 1.9% | 3,507.2 | 130.8 | 3.7% | _starpu_cpu_driver_run_once
> || 1.9% | 3,469.6 | 128.4 | 3.7% | _starpu_may_pause

Note that these are "idle" functions actually, i.e. StarPU is just
looking for things to do due to lack of parallelism. This is not a sign
of overhead.

> We reduced then the number of worker threads per node to 16 and 8: we
> recover
> our parallel efficiency up to a decent level!

But did it achieve the computation faster?

In other words, you may just not have enough parallelisme to feed all
these threads.

> we would expect threads to stay idle and not consume resources.

To provide good latency, StarPU does not leave resources idle, they take
work to be done as quickly as possible.

Samuel




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