46 lines
1.6 KiB
Diff
46 lines
1.6 KiB
Diff
From dc8c5d3ba8ec3c2de8ca0898d682d89492d275b3 Mon Sep 17 00:00:00 2001
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From: Shuo Wang <wangshuo_1994@foxmail.com>
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Date: Tue, 2 Mar 2021 10:41:09 +0800
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Subject: [PATCH] turn REP_STOSB_THRESHOLD from 2k to 1M
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REP_STOSB_THRESHOLD is designed to choose vec mov or stosb.
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The default threshold (2k) will lead to performance degradation if the
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memcpy size is between 2k and 1M.
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---
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sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S | 12 +++++++++++-
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1 file changed, 11 insertions(+), 1 deletion(-)
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diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
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index faa40856..76f84748 100644
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--- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
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+++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
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@@ -58,6 +58,16 @@
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# endif
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#endif
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+/* Threshold to use Enhanced REP STOSB. Since there is overhead to set
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+ up REP STOSB operation, REP STOSB isn't faster on short data. The
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+ memset micro benchmark in glibc shows that 2KB is the approximate
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+ value above which REP STOSB becomes faster on processors with
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+ Enhanced REP STOSB. Since the stored value is fixed, larger register
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+ size has minimal impact on threshold. */
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+#ifndef REP_STOSB_THRESHOLD
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+# define REP_STOSB_THRESHOLD 1048576
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+#endif
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+
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#ifndef SECTION
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# error SECTION is not defined!
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#endif
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@@ -171,7 +181,7 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
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ret
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L(stosb_more_2x_vec):
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- cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
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+ cmp $REP_STOSB_THRESHOLD, %RDX_LP
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ja L(stosb)
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#endif
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L(more_2x_vec):
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--
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2.23.0
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