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131 lines
5.9 KiB
131 lines
5.9 KiB
commit cecbac52123456e2fbcff062a4165bf7b9174797 |
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Author: Noah Goldstein <goldstein.w.n@gmail.com> |
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Date: Mon Nov 1 00:49:52 2021 -0500 |
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x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h |
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No bug. |
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This patch doubles the rep_movsb_threshold when using ERMS. Based on |
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benchmarks the vector copy loop, especially now that it handles 4k |
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aliasing, is better for these medium ranged. |
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On Skylake with ERMS: |
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Size, Align1, Align2, dst>src,(rep movsb) / (vec copy) |
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4096, 0, 0, 0, 0.975 |
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4096, 0, 0, 1, 0.953 |
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4096, 12, 0, 0, 0.969 |
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4096, 12, 0, 1, 0.872 |
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4096, 44, 0, 0, 0.979 |
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4096, 44, 0, 1, 0.83 |
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4096, 0, 12, 0, 1.006 |
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4096, 0, 12, 1, 0.989 |
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4096, 0, 44, 0, 0.739 |
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4096, 0, 44, 1, 0.942 |
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4096, 12, 12, 0, 1.009 |
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4096, 12, 12, 1, 0.973 |
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4096, 44, 44, 0, 0.791 |
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4096, 44, 44, 1, 0.961 |
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4096, 2048, 0, 0, 0.978 |
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4096, 2048, 0, 1, 0.951 |
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4096, 2060, 0, 0, 0.986 |
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4096, 2060, 0, 1, 0.963 |
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4096, 2048, 12, 0, 0.971 |
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4096, 2048, 12, 1, 0.941 |
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4096, 2060, 12, 0, 0.977 |
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4096, 2060, 12, 1, 0.949 |
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8192, 0, 0, 0, 0.85 |
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8192, 0, 0, 1, 0.845 |
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8192, 13, 0, 0, 0.937 |
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8192, 13, 0, 1, 0.939 |
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8192, 45, 0, 0, 0.932 |
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8192, 45, 0, 1, 0.927 |
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8192, 0, 13, 0, 0.621 |
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8192, 0, 13, 1, 0.62 |
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8192, 0, 45, 0, 0.53 |
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8192, 0, 45, 1, 0.516 |
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8192, 13, 13, 0, 0.664 |
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8192, 13, 13, 1, 0.659 |
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8192, 45, 45, 0, 0.593 |
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8192, 45, 45, 1, 0.575 |
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8192, 2048, 0, 0, 0.854 |
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8192, 2048, 0, 1, 0.834 |
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8192, 2061, 0, 0, 0.863 |
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8192, 2061, 0, 1, 0.857 |
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8192, 2048, 13, 0, 0.63 |
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8192, 2048, 13, 1, 0.629 |
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8192, 2061, 13, 0, 0.627 |
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8192, 2061, 13, 1, 0.62 |
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Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com> |
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com> |
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(cherry picked from commit 475b63702ef38b69558fc3d31a0b66776a70f1d3) |
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diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h |
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index e6c94dfd023a25dc..2e43e67e4f4037d3 100644 |
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--- a/sysdeps/x86/dl-cacheinfo.h |
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+++ b/sysdeps/x86/dl-cacheinfo.h |
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@@ -866,12 +866,14 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) |
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/* NB: The REP MOVSB threshold must be greater than VEC_SIZE * 8. */ |
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unsigned int minimum_rep_movsb_threshold; |
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#endif |
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- /* NB: The default REP MOVSB threshold is 2048 * (VEC_SIZE / 16). */ |
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+ /* NB: The default REP MOVSB threshold is 4096 * (VEC_SIZE / 16) for |
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+ VEC_SIZE == 64 or 32. For VEC_SIZE == 16, the default REP MOVSB |
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+ threshold is 2048 * (VEC_SIZE / 16). */ |
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unsigned int rep_movsb_threshold; |
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if (CPU_FEATURE_USABLE_P (cpu_features, AVX512F) |
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&& !CPU_FEATURE_PREFERRED_P (cpu_features, Prefer_No_AVX512)) |
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{ |
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- rep_movsb_threshold = 2048 * (64 / 16); |
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+ rep_movsb_threshold = 4096 * (64 / 16); |
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#if HAVE_TUNABLES |
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minimum_rep_movsb_threshold = 64 * 8; |
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#endif |
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@@ -879,7 +881,7 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) |
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else if (CPU_FEATURE_PREFERRED_P (cpu_features, |
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AVX_Fast_Unaligned_Load)) |
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{ |
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- rep_movsb_threshold = 2048 * (32 / 16); |
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+ rep_movsb_threshold = 4096 * (32 / 16); |
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#if HAVE_TUNABLES |
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minimum_rep_movsb_threshold = 32 * 8; |
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#endif |
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diff --git a/sysdeps/x86/dl-tunables.list b/sysdeps/x86/dl-tunables.list |
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index dd6e1d65c9490d4f..419313804d49cf65 100644 |
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--- a/sysdeps/x86/dl-tunables.list |
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+++ b/sysdeps/x86/dl-tunables.list |
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@@ -32,17 +32,21 @@ glibc { |
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} |
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x86_rep_movsb_threshold { |
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type: SIZE_T |
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- # Since there is overhead to set up REP MOVSB operation, REP MOVSB |
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- # isn't faster on short data. The memcpy micro benchmark in glibc |
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- # shows that 2KB is the approximate value above which REP MOVSB |
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- # becomes faster than SSE2 optimization on processors with Enhanced |
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- # REP MOVSB. Since larger register size can move more data with a |
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- # single load and store, the threshold is higher with larger register |
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- # size. Note: Since the REP MOVSB threshold must be greater than 8 |
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- # times of vector size and the default value is 2048 * (vector size |
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- # / 16), the default value and the minimum value must be updated at |
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- # run-time. NB: Don't set the default value since we can't tell if |
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- # the tunable value is set by user or not [BZ #27069]. |
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+ # Since there is overhead to set up REP MOVSB operation, REP |
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+ # MOVSB isn't faster on short data. The memcpy micro benchmark |
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+ # in glibc shows that 2KB is the approximate value above which |
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+ # REP MOVSB becomes faster than SSE2 optimization on processors |
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+ # with Enhanced REP MOVSB. Since larger register size can move |
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+ # more data with a single load and store, the threshold is |
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+ # higher with larger register size. Micro benchmarks show AVX |
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+ # REP MOVSB becomes faster apprximately at 8KB. The AVX512 |
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+ # threshold is extrapolated to 16KB. For machines with FSRM the |
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+ # threshold is universally set at 2112 bytes. Note: Since the |
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+ # REP MOVSB threshold must be greater than 8 times of vector |
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+ # size and the default value is 4096 * (vector size / 16), the |
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+ # default value and the minimum value must be updated at |
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+ # run-time. NB: Don't set the default value since we can't tell |
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+ # if the tunable value is set by user or not [BZ #27069]. |
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minval: 1 |
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} |
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x86_rep_stosb_threshold {
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