[petsc-dev] Question about MPICH device we use

[Jed Brown]

I think we should default to ch3:nemesis when --download-mpich, and only do ch3:sock when requested (which we would do in CI).

Satish Balay via petsc-dev <petsc-dev at mcs.anl.gov> writes:

> Primarily because ch3:sock performance does not degrade in oversubscribe mode - which is developer friendly - i.e on your laptop.
>
> And folks doing optimized runs should use a properly tuned MPI for their setup anyway.
>
> In this case --download-mpich-device=ch3:nemesis is likely appropriate if using --download-mpich [and not using a separate/optimized MPI]
>
> Having defaults that satisfy all use cases is not practical.
>
> Satish
>
> On Wed, 22 Jul 2020, Matthew Knepley wrote:
>
>> We default to ch3:sock. Scott MacLachlan just had a long thread on the
>> Firedrake list where it ended up that reconfiguring using ch3:nemesis had a
>> 2x performance boost on his 16-core proc, and noticeable effect on the 4
>> core speedup.
>> 
>> Why do we default to sock?
>> 
>>   Thanks,
>> 
>>      Matt
>> 
>>