Re: [Starpu-devel] StarPU+SimGrid: FetchingInput computation

[Luka Stanisic <luka.stanisic@inria.fr>]

Hello Mirko,

Indeed, 50% prediction error is quite big and it suggests that something 
is probably not correctly configured. Could you please send us a 
compressed version of you ".starpu/sampling" folder, the one from which 
simulation will read the performance models. This can help us get the 
first ideas of the machine and application you are trying to simulate.

To answer your question, the fetching time is computed based on the size 
of the data being transfered, latency and bandwidth of the link (in 
machine.platform.xml file) and the possible contention due to other 
transfers occurring in parallel.

Best regards,
Luka

On 07/12/2016 12:50, Mirko Myllykoski wrote:
> Hi,
>
> my name is Mirko Myllykoski and I work as a PostDoc researcher for the 
> NLAFET project at Umeå University.
>
> I am currently implementing a (shared memory) numerical software using 
> StarPU and I am trying to simulate my code using SimGrid. However, I 
> noticed that the simulated execution time is way off (about 50%). I 
> checked the generated FxT traces using vite and it seems that SimGrid 
> introduces too much fetching time (State: FetchingInput) to the 
> simulation.
>
> How is this fetching time being computed? My performance models 
> include the starpu_perfmodel::size_base data field and I guess that 
> information is somehow used to compute the fetch time.
>
> Best Regards,
> Mirko Myllykoski
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