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Simplifying fallback kernels #303

Merged
merged 3 commits into from
Sep 21, 2023
Merged

Simplifying fallback kernels #303

merged 3 commits into from
Sep 21, 2023

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manodeep
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Reduced the amount of code in the fallback kernels. At least on my M2 laptop, it runs faster - slightly faster (5-10%) for DD-type (i.e. small number-density) and significantly (~20-25%) faster for RR-type calculations

@manodeep manodeep mentioned this pull request Aug 23, 2023
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@manodeep manodeep requested a review from lgarrison August 29, 2023 00:38
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@lgarrison Didn't realise I hadn't requested a review -- oops!

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Ohh forgot to mention that I ran the INTEGRATION_TESTS for this change and the exhaustive tests passed

lgarrison
lgarrison approved these changes Aug 29, 2023
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All looks fine to me! Did you do any tests to figure out where the speedup is coming from?

mocks/DDrppi_mocks/countpairs_rp_pi_mocks_kernels.c.src
npairs[ibin]++;
if(need_rpavg) {
rpavg[ibin]+=rp;
src_npairs[ibin]++;
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I guess the idea here is that there's no point in making stack buffers, since the passed buffers are already local to the current thread?

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Yup. I am also considering whether it would be worthwhile to move to a malloc'ed buffer rather than the stack (but there may be side-effects of false sharing under OpenMP with such a malloc'ed src_npairs[nthreads][nbins] kind of matrix)

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Didn't actually do a line-by-line comparison timer. Will attempt to do that on my laptop; plus, I will also check that the runtime is not adversely affected on our local linux supercomputer (Skylake and AMD EPYC)

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Timed the tests on the master and this branch on Skylake cpus - essentially no difference for theory but the mocks, specifically DDtheta is faster.

Timed the tests on master vs this branch on EPYC cpus - same as above difference in theory but slightly faster with the simplified kernels (but smaller improvements compared to SKX). In general, both branches run faster on EPYC compared to SKX.

@manodeep manodeep merged commit e72cf70 into master Sep 21, 2023
@manodeep manodeep deleted the simplify_fallback branch September 21, 2023 12:10
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Totally forgot to merge this PR!

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manodeep commented May 2, 2024

Commenting to add the link to the original #296 that spurred this work

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