Relax scratch space limits for HIP reductions #6029
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Change-Id: I66c73cb3e53b99d8d0b59f423ae77263ca7e176f
Change-Id: I1400b8e9bc8c0a5af237283e7fc4db641d05b3f8
Rombur
approved these changes
Mar 31, 2023
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@arghdos nice catch! |
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I re-ran exercise 4 from the tutorials. Still not the nice plateau we'd like to see but it does look better with this PR. |
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That was next on my list of things to check :), I'll re-run my profiling on the new (smaller) dip and see if we can iron it out further |
dalg24
approved these changes
Apr 3, 2023
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Ignoring clearly unrelated GCC-8.4.0 failure |
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This change is motivated by profiling of some LJ reduction kernels in LAMMPS. Essentially we noticed that in some cases, we ended up severely occupancy limited by the "gridDim <= blockDim" restriction. Omniperf showed very low L1/L2 utilization, but the limiter was simply that we were not launching enough blocks.
This is a simple change to relax the scratch space limit slightly (from blockDim to 4096) to increase occupancy, but still keep the scratch limits well bounded. I was not particularly scientific about choosing the new limit, and I'm definitely open to better heuristics, but this increased RHODO (4^3) perf in LAMMPS by ~28% (the key kernel is a ParReduce)