[petsc-users] Very poor speed up performance

[Matthew Knepley]

On Mon, Dec 20, 2010 at 8:46 AM, Yongjun Chen <yjxd.chen at gmail.com> wrote:

>
> Hi everyone,
>
>
> I use PETSC (version 3.1-p5) to solve a linear problem Ax=b. The matrix A
> and right hand vector b are read from files. The dimension of A is
> 1.2Million*1.2Million. I am pretty sure the matrix A and vector b have been
> read correctly.
>
> I compiled the program with optimized version (--with-debugging=0), tested
> the speed up performance on two servers, and I have found that the
> performance is very poor.
>
> For the two servers, one is 4 cpus * 4 cores per cpu, i.e., with a total 16
> cores. And the other one is 4 cpus * 12 cores per cpu, with a total 48
> cores.
>
> On each of them, with the increasing of computing cores k from 1 to 8
> (mpiexec –n  k ./Solver_MPI -pc_type jacobi -ksp-type gmres), the speed up
> will increase from 1 to 6, but when the computing cores k increase from 9 to
> 16(for the first server) or 48 (for the second server), the speed up
> decrease firstly and then remains a constant value 5.0 (for the first
> server) or 4.5(for the second server).
>

We cannot say anything at all without -log_summary data for your runs.

   Matt


>  Actually, the program LAMMPS speed up excellently on these two servers.
>
> Any comments are very appreciated! Thanks!
>
>
>
>
> --------------------------------------------------------------------------------------------------------------------------
>
> PS: the related codes are as following,
>
>
> //firstly read A and b from files
>
> ...
>
> //then
>
>
>
>               ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
> CHKERRQ(ierr);
>
>               ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>
>               ierr = VecAssemblyBegin(b); CHKERRQ(ierr);
>
>               ierr = VecAssemblyEnd(b); CHKERRQ(ierr);
>
>
>
>               ierr = MatSetOption(A,MAT_SYMMETRIC,PETSC_TRUE);
> CHKERRQ(ierr);
>
>               ierr = MatGetRowUpperTriangular(A); CHKERRQ(ierr);
>
>               ierr = KSPCreate(PETSC_COMM_WORLD,&ksp);CHKERRQ(ierr);
>
>
>
>               ierr =
> KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);CHKERRQ(ierr);
>
>               ierr = KSPGetPC(ksp,&pc);CHKERRQ(ierr);
>
>               ierr =
> KSPSetTolerances(ksp,1.e-7,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);CHKERRQ(ierr);
>
>               ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr);
>
>
>
>               ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr);
>
>
>
>               ierr = KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
>
>
>
>               ierr = KSPGetSolution(ksp, &x);CHKERRQ(ierr);
>
>
>
>               ierr = VecAssemblyBegin(x);CHKERRQ(ierr);
>
>               ierr = VecAssemblyEnd(x);CHKERRQ(ierr);
>
> ...
>
>
>
>


-- 
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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