On 28, Jun 2007, at 8:44 PM, Jason House wrote:
Darren Cook wrote:
Can MPI be as quick as threads on a 2- or 4-core single
machine?
no, but I think you are worried about something that is such a a
small percentage of compute time that I doubt that it is significant
for a Go program. I would suggest you use MPI if you already know and
like it, and use threads if you already know that. If this is an
opportunity to learn, then I'd learn threads for a single multicore
machine.
The usage of MPI that I've seen required explicit population of
(user-defined) communication structures that get copied in the
process of doing an MPI call.
This is true and something we tried to put some wrappers around to
simplify, but this underlying fact could not be removed. I think it
is a pain that whenever we want to modify the message we have to go
down a few layers and tell MPI the number of integers and floats we
are going to pass. It led to a few debugging headaches when we
started, but we are used to it now. Whenever a struct changes we
check to see if it is in any messages.
But SlugGo runs on a cluster of many boxes, so threading is not a
choice for us. But once the code uses MPI, it works just fine across
the network or in the same CPU.
I really didn't want to manually specify, populate, and then read
out data for any given inter-process call. I ended up using
delegates / functors for inter-process communication and restricted
the bot to threading to keep the work to implement it simple.
Maybe after doing enough multi-threaded programming I'll come to
realize that MPI isn't much of a cost and shift my IPC design to
use MPI. In the mean time, I'm comforted that allowing slug go
support can bridge the gap if needed.
What about if a heavy playout algorithm is using a pattern library
too
big to fit in the cores local cache? Would that change the MPI vs.
threads decision?
Not to me.
Cheers,
David
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