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

[Matthew Knepley]

On Tue, Mar 13, 2012 at 3:22 PM, Dave May <dave.mayhem23 at gmail.com> wrote:

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

They have to be substantial, but it depends on your arithmetic intensity.
What I can say
for sure is that we maxed out the memory on the machines we have (like my
laptop) and
saw 3-5x speed up with SpMV.

Also, I saw a TON of overhead on my FEM benchmark, even though it is
screaming on
the GPU, but I now think that is cudaMalloc()/Free() rather than all
communication.

   Matt


> 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
>



-- 
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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