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

[Matthew Knepley]

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
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