[gmx-developers] Double Precision on GPUs

[Michael R Shirts]

  *   I think that in many cases the single precision force computation is not what is limiting the accuracy. It is rather the integration and in particular the constraints using single precision.

I recall talking over old results with Erik (many years ago) that showed exactly this, and seem to have been found by other people; integration and constraints cannot really be done well in single precision; but if they are in double precision (or even mixed precision, with careful analysis of rounding steps), with the force in single precision, then numerical performance is much, much better.

Best,
~~~~~~~~~~~~~~~~
Michael Shirts
Associate Professor
michael.shirts at colorado.edu<mailto:michael.shirts at colorado.edu>
http://www.colorado.edu/lab/shirtsgroup/
Phone: (303) 735-7860
Office: JSCBB C123
Department of Chemical and Biological Engineering
University of Colorado Boulder


From: <gromacs.org_gmx-developers-bounces at maillist.sys.kth.se> on behalf of Berk Hess <hess at kth.se>
Reply-To: "gmx-developers at gromacs.org" <gmx-developers at gromacs.org>
Date: Wednesday, July 31, 2019 at 8:42 AM
To: "gmx-developers at gromacs.org" <gmx-developers at gromacs.org>
Subject: Re: [gmx-developers] Double Precision on GPUs

Hi,

I think that in many cases the single precision force computation is not what is limiting the accuracy. It is rather the integration and in particular the constraints using single precision. Another solution is to have integration and constraints in double precision and (parts of) the force computation in single precision.

Cheers,

Berk

On 7/31/19 4:35 PM, David Lister wrote:
Hello,

Sorry this isn't part of the email thread from earlier, I found the thread in the archives and decided to chime in. Not sure how to reply to old threads, but the link is here for consistency. https://mailman-1.sys.kth.se/pipermail/gromacs.org_gmx-developers/2019-July/010488.html

I am also be very interested in having double precision supported on GPUs. I'm using gromacs for a project that stretches the target use case and have found the single precision just doesn't give good results. The same simulation run in both single and double gives different results, with the double precision simulation giving the results expected by theory. Unfortunately though, double precision is much slower.

Having GPU support for double precision would be a really big help for me as well.

Cheers,
David




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-developers/attachments/20190731/4305a4c8/attachment-0001.html>