[petsc-dev] Generality of VecScatter

[Jed Brown]

On Tue, Nov 29, 2011 at 08:52, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> >From what I understand Barry doesn't want the threads to spin.
>

Lots of MPI calls spin because it's MUCH lower latency. Unless we have more
threads than cores, what is the problem?


> Also, synchronizing through an unguarded memory location seems to create a
> race conditions.
>

Not if writes are atomic. There is always a way to do atomic writes
(usually machine-word) because otherwise the operating system could not
implement synchronization primitives.

Isn't cmpxchg instruction-set specific?
>

All instruction sets have some analogue of cmpxchg because it's the
building block for all other primitives.
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