[mpiwg-rma] Atomicity of Accumulates

[maik peterson]

simon, on most systems today there is no way to sync userlevel libs like mpi
with isa instructions in terms of atomicity. if you want perf. do it by
hand:
i) separate them
ii) merge them with hand-crafted methods within threads

several order faster than mpi sequentializing...
mp


2017-08-16 11:24 GMT+02:00 Simon Schwitanski <
simon.schwitanski at rwth-aachen.de>:

> Hello,
>
> I have got a question about the atomicity of accumulate operations as
> described in 11.7.1. It says (page 461, lines 8 - 11):
>
> > The previous correctness conditions imply that a location updated by a
> > call to an accumulate operation cannot be accessed by a load or an RMA
> > call other than accumulate until the accumulate operation has completed
> > (at the target).
>
> I am a little bit confused about what this actually means: Does it mean
> that local load accesses on the target are (somehow) delayed if there is
> an ongoing accumulate operation to the same location? Or does it just
> mean that concurrent load accesses are forbidden and lead to undefined
> behavior? And why does this not hold for store accesses?
>
> Thanks!
>
>
> Simon
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