[mpich-discuss] Faster MPI_Attr_get?

[Jeff Hammond]

> I benchmarked an example using the PETSc ThreadComm. For a micro-benchmark
> that doesn't use pthreads, I would just call MPI_Attr_get() in a loop. I can
> prepare that if you like.

that's probably greatly underestimating the cost of this function
since i assume in this test every time the function is called, both
the dcache and icache hit every time.

>> Also, please send me the configure options that you are using for your
>> MPICH2 under petsc.  The absolute performance is going to vary substantially
>> depending on whether error checking is enabled and your choice of a few
>> other options.
>
>
> I tested these two configurations, what do you suggest I use if I want that
> function to be fast?
>
> MPICH2 Version:         1.4
> MPICH2 Release date:    Thu Jun 16 16:41:08 CDT 2011
> MPICH2 Device:          ch3:nemesis
> MPICH2 configure:       --prefix=/opt/mpich2 --enable-shared
> --enable-sharedlibs=gcc --enable-error-checking=runtime
> --enable-error-messages=all --enable-timer-type=clock_gettime
> --with-python=python2
> MPICH2 CC:      gcc  -march=native -O1 -pipe  -O2
> MPICH2 CXX:     c++  -march=native -O1 -pipe -O2
> MPICH2 F77:     gfortran   -O2
> MPICH2 FC:      gfortran   -O2

Is "-O2" a suboption to "-pipe" or are you giving the compiler
conflicting flags?

> MPICH2 Version:     1.5b1
> MPICH2 Release date: unreleased development copy
> MPICH2 Device:     ch3:nemesis
> MPICH2 configure: --prefix=/homes/jedbrown/usr/mpich-intel --enable-shared
> --enable-error-checking=runtime --enable-error-messages=all
> --enable-timer-type=clock_gettime CC=icc CXX=icpc --enable-fc=0
> --enable-f77=0 FC= F77=
> MPICH2 CC: icc    -O2
> MPICH2 CXX: icpc   -O2
> MPICH2 F77: gfortran
> MPICH2 FC: gfortran

"--enable-error-checking=runtime --enable-error-messages=all" would
seem to be the kind of thing Dave is talking about that affect
performance.

Jeff


-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
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