I don't disagree with your methods at all and I'm sure you got a lot of
benefit from it, but GPUs are qualitatively different beasts from CPUs in
that they are internally massively parallel, with each of them equal to ~50
modern CPU cores.
There is a great deal of deterministic dynamic load-balancing going on
internally within each GPU because of this. Having done so, this leaves
only table scraps for further load-balancing between GPUs.
The only scenario where this would be of significant benefit is when GPUs
with significantly different performance were mixed together in a parallel
run. But given this seems to be a corner case scenario and I only have
limited cycles for adding AMBER functionality, it's of very low priority.
Scott
On Wed, Sep 19, 2012 at 12:03 PM, Duke, Robert E Jr <rduke.email.unc.edu>wrote:
> Another comment - the way I tested this stuff was to include code that
> forced very rapid rebalance (for test only). That way, I could see
> balancing effects within the time window that dynamics does not drift due
> to fp rounding error.
> - Bob
> ________________________________________
> From: Scott Le Grand [varelse2005.gmail.com]
> Sent: Wednesday, September 19, 2012 11:18 AM
> To: AMBER Mailing List
> Subject: Re: [AMBER] Loading across GPUs
>
> And PS anything but static load balancing would lead to nondeterministic
> execution and that's a dealbreaker for my inner software engineer...
> On Sep 19, 2012 5:50 AM, "Jason Swails" <jason.swails.gmail.com> wrote:
>
> >
> >
> > On Sep 19, 2012, at 5:57 AM, Adam Jion <adamjion.yahoo.com> wrote:
> >
> > > Hi,
> > >
> > > Is it possible to control the computational loading across the GPUs for
> > a multi-GPU run of Amber?
> > > That is, I want GPU 1 to do 75% of the computation whilst GPU 2 does
> 25%
> > of the computation.
> >
> > No. The only reason I could imagine wanting to try this is if the 2 GPUs
> > are different and one is slower.
> >
> > If this is the case, you basically have to use them for different
> > simulations. For parallel sims, because of the serial nature of Molecular
> > Dynamics, a parallel job could very easily be slower than one run on the
> > fastest GPU (since it will be waiting for the slowest one to finish).
> >
> > HTH,
> > Jason
> >
> > --
> > Jason M. Swails
> > Quantum Theory Project,
> > University of Florida
> > Ph.D. Candidate
> > 352-392-4032
> > _______________________________________________
> > AMBER mailing list
> > AMBER.ambermd.org
> > http://lists.ambermd.org/mailman/listinfo/amber
> >
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Received on Wed Sep 19 2012 - 15:00:02 PDT
