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[charm] Order of central call from distributed functions


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  • From: François Tessier <francois.tessier AT inria.fr>
  • To: "charm AT cs.uiuc.edu" <charm AT cs.uiuc.edu>
  • Subject: [charm] Order of central call from distributed functions
  • Date: Wed, 30 Oct 2013 17:42:40 +0100
  • List-archive: <http://lists.cs.uiuc.edu/pipermail/charm/>
  • List-id: CHARM parallel programming system <charm.cs.uiuc.edu>

Hello,

On the distributed version of my load balancer, I observe a weird
behavior and I would like to have your opinion about that. My code looks
like this :

--------------------------------------
MyLB::work() {
for (int i=7; i>=0; i--) { // Desc. order

CProxy_MyLB(thisgroup)[CmiGetFirstPeOnPhysicalNode(i)].DistFunction(i);
}
}

MyLB::DistFunction (int i) {
// ... Do some calculation
fprintf(stderr, "Dist %d", i);
CProxy_MyLB(thisgroup)[0].CentralFunction(i);
}

MyLB::CentralFunction (int i) {
fprintf(stderr, "Central %d", i);
//... Do some calculation
}
-----------------------------------------

And when I execute that, the output is always something like that :

Dist 7
Dist 6
Dist 5
Dist 4
Dist 3
Dist 2
Dist 1
Dist 0
Central 0
Central 1
Central 2
Central 3
Central 4
Central 5
Central 6
Central 7

So, each distributed function is called in desc order as specified by my
for loop. But even if each distributed function calls the central one
with the same order, this central function is carried out in a reverse
way... You'll find as an attachment a Gantt chart which illustrate that
(The R part corresponds to a wait time and the P part corresponds to the
central calculation).

I hope it's clear :) It's not very easy to explain...

How can we explain this behavior?

Thanks

François

--
___________________
François TESSIER
PhD Student at University of Bordeaux
Inria - Runtime Team
Tel : 0033.5.24.57.41.52
francois.tessier AT inria.fr
http://runtime.bordeaux.inria.fr/ftessier/
PGP 0x8096B5FA

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