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

[Xiangze Zeng]

Hi, Matt.


I get it. I just test a so little system. I'll try a larger one.


Zeng

在 2012-03-13 22:03:12，"Matthew Knepley" <knepley at gmail.com> 写道：
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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