[petsc-users] Fwd: direct solvers on KNL

[Matthew Knepley]

On Fri, Sep 1, 2017 at 7:40 AM, Jakub Kruzik <jakub.kruzik at vsb.cz> wrote:

> Hi,
>
> I am looking at a single node performance of MUMPS and SuperLU on KNL 7230
> (on Theta). I am using KSP example ex2 (http://www.mcs.anl.gov/petsc/
> petsc-current/src/ksp/ksp/examples/tutorials/ex2.c.html) with m X n =
> 2880 x 2880. KNL runs in cache and quad modes.
>
> Times in seconds for 24 cores:
> mumps:   279
> superlu:   326
> cg:             116
>
> Times in seconds for 64 cores:
> mumps:   316
> superlu:   410
> cg :            49
>
> The performance for 24 cores is OK - both direct solvers are roughly 3.5
> times slower than 2x E5-2680v3. (According to people from Intel, the single
> core performance of KNL is about 3-4 times lower than that of E5-2680v3).
> However, strong scalability is really bad.
>
> I am using cray-petsc/3.7.6.0 module. I tried my own PETSc compilation
> with MKL and MUMPS/SuperLU installed by PETSc configure but the results are
> similar.
>
> Please find attached Theta submission script and logs for KNL and Haswells.
>
> Why the performance of direct solvers on a full node is so bad?
>

Admittedly it was for different computations, but we saw strong scaling
degradation after 32 cores of KNL
in https://arxiv.org/abs/1705.09907, and we also saw strong scaling tail
off as the problem size got this small
in https://arxiv.org/abs/1705.03625

   Thanks,

     Matt


> Best,
> Jakub
>



-- 
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

http://www.caam.rice.edu/~mk51/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20170901/5d7888bb/attachment.html>