[petsc-users] Optimised vs Debug

Jed Brown jedbrown at mcs.anl.gov
Tue Dec 13 15:19:42 CST 2011

On Tue, Dec 13, 2011 at 13:16, Bogdan Dita <bogdan at lmn.pub.ro> wrote:

> So I reconfigured PETSc as advised, the result was that the time obtained
> from the new version of PETSc Optimised version(with COPTFLAGS) was about
> the same as the time from the Debug version(+/- 2 sec).

You have to send output from -log_summary in both cases if you want us to
help explain observed performance.

> Although is not
> what I expected this is still an intriguing result for me: on one hand
> there was definitely something about the flags that the optimised PETSc
> didn't like, exactly how Mr. J. Brown predicted, but on the other hand
> this raises new questions.
> This is the output from 'mpicc -show'.
> for the cluster:
> gcc -m64 -O2 -fPIC -Wl,-z,noexecstack -I/usr/include/mpich2-x86_64
> -L/usr/lib64/mpich2/lib -lmpich

This one is optimized by default.

> and from my laptop:
> gcc -I/usr/lib64/mpich2/include -L/usr/lib64/mpich2/lib
> -Wl,-rpath,/usr/lib64/mpich2/lib -lmpich -lopa -lmpl -lrt -lpthread

This one is not.

PETSc folks, should we fight MPICH2 by explicitly adding -O0 for debug
builds in which CFLAGS are not passed by the user?
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