[petsc-users] CPU vs GPU for PETSc applications

[Justin Chang]

Matt,

So what's an example of "doing a bunch of iterations to make sending the
initial datadown worth it"? Is there a correlation between that and
arithmetic intensity, where an application is likely to be more
compute-bound and memory-bandwidth bound?

Thanks,
Justin

On Thu, Mar 10, 2016 at 2:50 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Mar 10, 2016 at 12:29 PM, Justin Chang <jychang48 at gmail.com>
> wrote:
>
>> Hi all,
>>
>> When would I ever use GPU computing for a finite element simulation where
>> the limiting factor of performance is the memory bandwidth bound? Say I
>> want to run problems similar to SNES ex12 and 62. I understand that there
>> is an additional bandwidth associated with offloading data from the CPU to
>> GPU but is there more to it? I recall reading through some email threads
>> about GPU's potentially giving you a speed up of 3x that on a CPU but the
>> gain in performance may not be worth the increase in time moving data
>> around.
>
>
> The main use case is if you are being forced to use a machine which has
> GPUs. Then you can indeed get some benefit
> from the larger bandwidth. You need a problem where you are doing a bunch
> of iterations to make sending the initial data
> down worth it.
>
> It would certainly be better if you are computing the action of your
> operator directly on the GPU, but that is much more
> disruptive to the code right now.
>
>   Matt
>
>
>> Thanks,
>> Justin
>>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
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