From cf2c57526ba4b57e6863ad4db8a868e2678adce8 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 30 Apr 2021 05:58:59 -0700
Subject: [PATCH] x86: Set rep_movsb_threshold to 2112 on processors with FSRM
Content-type: text/plain; charset=UTF-8

The glibc memcpy benchmark on Intel Core i7-1065G7 (Ice Lake) showed
that REP MOVSB became faster after 2112 bytes:

                                      Vector Move       REP MOVSB
length=2112, align1=0, align2=0:        24.20             24.40
length=2112, align1=1, align2=0:        26.07             23.13
length=2112, align1=0, align2=1:        27.18             28.13
length=2112, align1=1, align2=1:        26.23             25.16
length=2176, align1=0, align2=0:        23.18             22.52
length=2176, align1=2, align2=0:        25.45             22.52
length=2176, align1=0, align2=2:        27.14             27.82
length=2176, align1=2, align2=2:        22.73             25.56
length=2240, align1=0, align2=0:        24.62             24.25
length=2240, align1=3, align2=0:        29.77             27.15
length=2240, align1=0, align2=3:        35.55             29.93
length=2240, align1=3, align2=3:        34.49             25.15
length=2304, align1=0, align2=0:        34.75             26.64
length=2304, align1=4, align2=0:        32.09             22.63
length=2304, align1=0, align2=4:        28.43             31.24

Use REP MOVSB for data size > 2112 bytes in memcpy on processors with
fast short REP MOVSB (FSRM).

	* sysdeps/x86/dl-cacheinfo.h (dl_init_cacheinfo): Set
	rep_movsb_threshold to 2112 on processors with fast short REP
	MOVSB (FSRM).
---
 sysdeps/x86/cacheinfo.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sysdeps/x86/cacheinfo.h b/sysdeps/x86/cacheinfo.h
index f72f634a..cc3941d3 100644
--- a/sysdeps/x86/cacheinfo.h
+++ b/sysdeps/x86/cacheinfo.h
@@ -430,6 +430,12 @@ init_cacheinfo (void)
       rep_movsb_threshold = 2048 * (16 / 16);
       minimum_rep_movsb_threshold = 16 * 8;
     }
+
+  /* NB: The default REP MOVSB threshold is 2112 on processors with fast
+     short REP MOVSB (FSRM).  */
+  if (CPU_FEATURE_USABLE_P (cpu_features, FSRM))
+    rep_movsb_threshold = 2112;
+
   if (cpu_features->rep_movsb_threshold > minimum_rep_movsb_threshold)
     __x86_rep_movsb_threshold = cpu_features->rep_movsb_threshold;
   else
-- 
GitLab

