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Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems
Chronologique Discussions
- From: Hatem Ltaief <hatem.ltaief@kaust.edu.sa>
- To: Samuel Thibault <samuel.thibault@inria.fr>
- 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 15:13:57 +0000
- Accept-language: en-GB, en-US
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Hi Samuel,
> 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.
The threads are indeed running out of work due to strong scaling mode of
operation.
>
>> 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?
YES
So this is the question: why does it run much faster with smaller number of
threads per node?
>
> 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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- [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Hatem Ltaief, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Samuel Thibault, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Hatem Ltaief, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Samuel Thibault, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Hatem Ltaief, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Sameh Abdulah, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Samuel Thibault, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Samuel Thibault, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Hatem Ltaief, 26/04/2018
- Re: [Starpu-devel] Performance profiling of tile low rank cholesky (HiCMA) with StarPU on distributed memory systems, Samuel Thibault, 26/04/2018
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