Re: [AMBER] Amber20 Performance on RTX (Turing): known problems, with a patch forthcoming

From: Tim Travers <>
Date: Tue, 21 Jul 2020 09:17:07 -0600

Hi Dave,

I wanted to inquire if the patch for Amber20 that you mentioned below will
be made available? We are currently using CUDA 10.2 on Turing cards and
have seen the same slowdown. Not sure if these cards are among those that
do not perform the thread synchronization, and so would not benefit here by
upgrading to CUDA 11.


On Fri, May 29, 2020 at 12:30 AM David Cerutti <> wrote:

> Dear Users,
> As has been shared on this listserv, many users are finding that Amber20 is
> not as fast on Turing architectures for PME simulations as Amber18. The
> source of this problem has now been identified, and indeed it affects much
> more than just Turing, but the 15-20% slowdown seen on Turing is merely the
> most severe case.
> The slowdown itself does NOT reflect any bugs or issues that would
> necessitate repeating experiments. The problem, rather, is that some
> future-proofing that our collaborators at NVIDIA kindly performed for us
> has led to more GPU effort in synchronization. The benefit of this is
> that, come CUDA 11 and the new Ampere chipset, pmemd.cuda is already
> prepared to run on the cards (at a substantially greater speed than is
> currently possible with a V100, which in my view competes with RTX-6000 for
> top dog). However, legacy chipsets that do not need to perform the
> synchronization required for CUDA 11 to work properly will suffer in
> performance.
> Contrary to what I warned yesterday afternoon, a fix is possible and we
> already have it. A compiler-specific directive will create separate code
> paths for the various chipsets and mask out the synchronization where it is
> not needed, recovering the Amber18 performance while still keeping the code
> in a state that is ready for the next architecture.
> I would like to thank Scott Legrand, Peng Wang, and others at NVIDIA who
> contributed either to the future-proofing or the short-term recovery
> effort. As you sit at home preparing your new simulations, please enjoy
> some ice cream or other simple treat while you await the forthcoming patch
> that will put Amber20 back where it should be on the benchmarks.
> Sincerely,
> Dave Cerutti
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Received on Tue Jul 21 2020 - 08:30:03 PDT
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