[gmx-developers] interesting read: exascale w/o threads
hess at kth.se
Thu Oct 8 13:36:15 CEST 2015
Interesting read. The essential message is:
"Thus, we believe that a discussion on threads versus processes boils
down to “shared everything by default” versus “shared nothing by default”.
We came to the same conclusion in a discussion some time ago. So the
choice doesn't affect performance, but it strongly affects the code.
For Gromacs I think it's still convenient to have processes+threads,
since we have many data structures with many small arrays that change at
domain decomposition time that are needed by all threads in a domain.
Sharing all these through MPI3 is tedious.
On 10/08/2015 01:04 PM, Szilárd Páll wrote:
> "We believe that portions of the HPC community have adopted the point
> of view that somehow threads are “necessary” in order to utilize such
> [manycore/SMP] systems, (1) without fully understanding the
> alternatives, including MPI 3 functionality, (2) underestimating the
> difficulty of utilizing threads efficiently, and (3) without
> appreciating the similarities of threads and processes. This short
> paper, due to space constraints, focuses exclusively on issue (3)
> since we feel it has gotten virtually no attention."
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