[Rtk-users] How to run the reconstruction on a specific GPU?

[Cyril Mory]

Hi Louie,

We have been investigating your question bit. A first possible solution, 
which may be sufficient for your needs, could be to set the 
CUDA_VISIBLE_DEVICES environment variable. You'll find details here :
http://www.acceleware.com/blog/cudavisibledevices-masking-gpus

Here are two scripts I used to run tests on our two-GPUs server:

######### First script #########
echo "Running two instances of rtkfdk without specifying a GPU"
CUDA_VISIBLE_DEVICES="0,1"
time rtkfdk -p . -r .*.his -o fdkBothGPUs_0.mha --hardware cuda -g 
geom.xml --dimension 512 &
time rtkfdk -p . -r .*.his -o fdkBothGPUs_1.mha --hardware cuda -g 
geom.xml --dimension 512 &

######### Second script #########
echo "Running two instances of rtkfdk, specifying which GPU to use for each"
echo 'CUDA_VISIBLE_DEVICES="0"; time rtkfdk -p . -r .*.his -o 
fdkGPU_0.mha --hardware cuda -g geom.xml --dimension 512 &' | bash
echo 'CUDA_VISIBLE_DEVICES="1"; time rtkfdk -p . -r .*.his -o 
fdkGPU_1.mha --hardware cuda -g geom.xml --dimension 512 &' | bash

######### End #############

On our server, which has two identical GPUs, these two scripts took the 
same time. It seems that, in the first script, rtkfdk somehow managed to 
detect that the first GPU was in use and ran on the second one. But I 
can't guarantee under which conditions this happens, and surely it's 
safer to use the second script.

This is the cheapest solution. If you need more than that, and you are 
ready to dive into the cuda filters' code as well as into the automatic 
transfers between CPU and GPU memory, do not hesitate to propose 
modifications of the RTK code.

Regards,
Cyril

On 09/15/2014 02:45 PM, Simon Rit wrote:
> Hi,
> Good question, I did not hear anybody working on multiple GPUs so far.
> It currently uses the first Cuda compatible device. I think you'll
> have to look up in the Cuda manual to see how to switch to another one
> but there is nothing available in the RTK lib yet. Don't hesitate to
> suggest some code changes to add this feature.
> Simon
>
> On Mon, Sep 15, 2014 at 2:09 PM, ghostcz <ghostcz at hotmail.com> wrote:
>> Dear Rtk users,
>>
>> How can I select one (or maybe more?) specific GPU to run my reconstruction?
>> It seems if I start a second instance of the reconstruction program, it will
>> run on the same GPU.
>>
>> Best regards,
>> Louie
>>
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Cyril Mory, Post-doc
CREATIS
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