Charm++ parallel programming system

[Jozsef Bakosi <jbakosi AT gmail.com>]

Thanks Phil, that's interesting. I guess that (at least partially) explains (I hope) the pretty unsatisfactory weak scaling behavior I'm getting with a simple particle (i.e., Monta Carlo) code.

Thanks for the clarification,

J

On Thu, Jul 9, 2015 at 12:35 PM, Phil Miller <mille121 AT illinois.edu> wrote:

You're exactly right - reductions locally combine the contributions of all chare array elements on each PE, and then in each process, and transmit a single message up a process tree to the root. At large machine scales, this isn't just faster, it's the difference between the code running at all, and crashing due to a message overload.

On Thu, Jul 9, 2015 at 1:10 PM, Jozsef Bakosi <jbakosi AT gmail.com> wrote:

Hi folks,

I suspect I know the answer to this question but I'd like some clarification on it.

What is the main difference between creating (a potentially large number of) individual chares and those calling back to a single host proxy or creating the workers instead as a chare array and using reduction. I assume the latter will do some kind of message aggregation under the hood (i.e., using a tree) and collect messages (in the form of an entry method arguments) from individual array elements and send only aggregated messages to the single host. Is this correct? If so, I guess, I should get better performance...

Thanks,

Jozsef

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