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 > >> > >> ? 2012-03-13 20:12:09?"Jed Brown" <jedbrown at mcs.anl.gov> ??? > >> > >> 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120313/5d3b307c/attachment.htm>
