Subject: Re: [Boost-users] Hybrid parallelism, no more + mpi+serialization, many questions
From: Matthias Troyer (troyer_at_[hidden])
Date: 2010-11-17 12:28:07
On 16 Nov 2010, at 20:41, James C. Sutherland wrote:
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> On Tue, Nov 16, 2010 at 10:22 AM, Hicham Mouline <hicham_at_[hidden]> wrote:
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>> 2. what are the pros/cons of loading the static data objects individually from each separate mpi process vs broadcasting the static data via MPI itself after only the master reads/sets up the static data?
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> It is easier to load them from disk on each process (you don't have to deal with serialization and passing the structure). Typically you will not see a performance problem if this is only a one-time startup cost and if you are not loading massive data files from a file system with weak IO capabilities onto very many MPI processes.
I would go with reading once and broadcasting, especially if, as was mentioned before, one aims at going to thousands of processes. No I/O system can scale, and implementing the broadcast is trivial: a single function call.
Matthias