Re: [Starpu-devel] Strange behaviour using GPUs

[Nathalie Furmento <nathalie.furmento@labri.fr>]

Xavier,

There was indeed a bug in 1.1.0rc1 which made dmda queues LIFOs . This 
has been fixed in the branch. We actually found out by seeing MAGMA 
performances dropping down.

Could you please try and let us know if that also fixes your problem? I 
am planning to release 1.1.0rc2 tomorrow, but you could also try by 
checking out the svn repository.

Thanks,

Nathalie

in On 09/07/2013 14:19, Xavier Lacoste wrote:
> Hello,
>
> I tried to compare ParSEC and StarPU using full machines (mirage) on PaStiX.
> We achieve to have good scaling with ParSEC by statically scheduling task on 
> GPUs.
> So, I tried to reproduce the same scheduling with StarPU 1.1.0rc1 and 
> obtained strange behavious.
> My GPUs take all there time FetchingInput and PushingOutputs.
>
> The output trace can be seen here : 
> http://img401.imageshack.us/img401/5213/1pb.png
> Or, on plafrim cluster :
> 9 CPUs + 3 GPUs
> /lustre/lacoste/rsync/log_mirage_AUDI_dmda+LLT+flop+cmin20+frat8+distFlop+selfCopy+fxt_9_3_4231_20130709_120332_crit2_0.5GPUmem.trace
> 10 + 2 :
> /lustre/lacoste/rsync/log_mirage_AUDI_dmda+LLT+flop+cmin20+frat8+distFlop+selfCopy+fxt_10_2_4231_20130709_120332_crit2_0.5GPUmem.trace
> 11 + 1 :
> /lustre/lacoste/rsync/log_mirage_AUDI_dmda+LLT+flop+cmin20+frat8+distFlop+selfCopy+fxt_11_1_4231_20130709_120332_crit2_0.5GPUmem.trace
> 12 + 0 :
> /lustre/lacoste/rsync/log_mirage_AUDI_dmda+LLT+flop+cmin20+frat8+distFlop+selfCopy+fxt_12_0_4231_20130709_120332_crit2_0.5GPUmem.trace
>
> The results are good with 12 CPUs + 0, adding 1 or 2 GPUs bring no loss, but 
> no gain either, adding three slows down the run time by a factor 10.
>
> Do you have any idea of what can explain this behaviour ?
>
> With a dynamic scheduling, GPUs are usefull with a small number of CPUs but 
> not with the whole machine.
> (My cost model may not be accurate enough for the moment... 
> http://img515.imageshack.us/img515/2348/njz.png)
>
> Thanks,
>
> XL.
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