[petsc-users] [petsc-maint #107932] run a simple example ex19 in src/snes/examples/tutorials

[Dave May]

Hey Matt,
  Do you have any guidance or ideas regarding how large the subdomains
should be to offset the cost of this copy?

Cheers,
  Dave


On 13 March 2012 15:03, Matthew Knepley <knepley at gmail.com> wrote:
> On Tue, Mar 13, 2012 at 8:59 AM, Xiangze Zeng <zengshixiangze at 163.com>
> wrote:
>>
>> Hi, Jed.
>> At the beginning and end of  the codes for setting the matrices values, I
>> add "printf", and compute the time of this period. It is much longer than
>> that when I don't use the GPU. I just guess the time is used for copping
>> data. My PCTYPE is sor. And 2000 iterations.  Do you have any suggestion
>> about this?
>
>
> 1) You do not have to guess. Use -log_summary, and there are explicit events
> for copying to the GPU
>
> 2) GPUs only really become effective for large systems due to this overhead.
> I suggest looking at the
>     performance and overhead as a function of system size.
>
>    Matt
>
>>
>> Zeng
>>
>> 在 2012-03-13 20:12:09，"Jed Brown" <jedbrown at mcs.anl.gov> 写道：
>>
>> 2012/3/13 Xiangze Zeng <zengshixiangze at 163.com>
>>>
>>> After I  configure PETSc using --with-precision=single, I can run both
>>> ex19 and my own code. Good news! But it seems lots of time is using for
>>> copping the data from CPU to GPU.
>>
>>
>> How are you measuring? What preconditioner are you using and how many
>> iterations are typically required?
>>
>>
>>
>
>
>
> --
> 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