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authorH.J. Lu <hjl.tools@gmail.com>2017-04-18 14:01:45 -0700
committerH.J. Lu <hjl.tools@gmail.com>2017-04-18 14:01:45 -0700
commit4cb334c4d6249686653137ec273d081371b3672d (patch)
tree0ddce19851595aeccad1caf222c91014f7817de2 /sysdeps/x86
parent1c53cb49de6d82d9469ccbd5aa0c55924502bd8b (diff)
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x86: Use AVX2 memcpy/memset on Skylake server [BZ #21396]
On Skylake server, AVX512 load/store instructions in memcpy/memset may
lead to lower CPU turbo frequency in certain situations.  Use of AVX2
in memcpy/memset has been observed to have improved overall performance
in many workloads due to the higher frequency.

Since AVX512ER is unique to Xeon Phi, this patch sets Prefer_No_AVX512
if AVX512ER isn't available so that AVX2 versions of memcpy/memset are
used on Skylake server.

	[BZ #21396]
	* sysdeps/x86/cpu-features.c (init_cpu_features): Set
	Prefer_No_AVX512 if AVX512ER isn't available.
	* sysdeps/x86/cpu-features.h (bit_arch_Prefer_No_AVX512): New.
	(index_arch_Prefer_No_AVX512): Likewise.
	* sysdeps/x86_64/multiarch/memcpy.S (__new_memcpy): Don't use
	AVX512 version if Prefer_No_AVX512 is set.
	* sysdeps/x86_64/multiarch/memcpy_chk.S (__memcpy_chk):
	Likewise.
	* sysdeps/x86_64/multiarch/memmove.S (__libc_memmove): Likewise.
	* sysdeps/x86_64/multiarch/memmove_chk.S (__memmove_chk):
	Likewise.
	* sysdeps/x86_64/multiarch/mempcpy.S (__mempcpy): Likewise.
	* sysdeps/x86_64/multiarch/mempcpy_chk.S (__mempcpy_chk):
	Likewise.
	* sysdeps/x86_64/multiarch/memset.S (memset): Likewise.
	* sysdeps/x86_64/multiarch/memset_chk.S (__memset_chk):
	Likewise.
Diffstat (limited to 'sysdeps/x86')
-rw-r--r--sysdeps/x86/cpu-features.c6
-rw-r--r--sysdeps/x86/cpu-features.h3
2 files changed, 8 insertions, 1 deletions
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index ae7f844f8b..f30918dd3b 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -224,10 +224,14 @@ init_cpu_features (struct cpu_features *cpu_features)
 	  |= bit_arch_AVX_Fast_Unaligned_Load;
 
       /* Since AVX512ER is unique to Xeon Phi, set Prefer_No_VZEROUPPER
-         if AVX512ER is available.  */
+         if AVX512ER is available.  Don't use AVX512 to avoid lower CPU
+	 frequency if AVX512ER isn't available.  */
       if (CPU_FEATURES_CPU_P (cpu_features, AVX512ER))
 	cpu_features->feature[index_arch_Prefer_No_VZEROUPPER]
 	  |= bit_arch_Prefer_No_VZEROUPPER;
+      else
+	cpu_features->feature[index_arch_Prefer_No_AVX512]
+	  |= bit_arch_Prefer_No_AVX512;
 
       /* To avoid SSE transition penalty, use _dl_runtime_resolve_slow.
          If XGETBV suports ECX == 1, use _dl_runtime_resolve_opt.  */
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index 1583d65345..85a39e7d70 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -39,6 +39,7 @@
 #define bit_arch_Prefer_ERMS			(1 << 19)
 #define bit_arch_Use_dl_runtime_resolve_opt	(1 << 20)
 #define bit_arch_Use_dl_runtime_resolve_slow	(1 << 21)
+#define bit_arch_Prefer_No_AVX512		(1 << 22)
 
 /* CPUID Feature flags.  */
 
@@ -118,6 +119,7 @@
 # define index_arch_Prefer_ERMS		FEATURE_INDEX_1*FEATURE_SIZE
 # define index_arch_Use_dl_runtime_resolve_opt FEATURE_INDEX_1*FEATURE_SIZE
 # define index_arch_Use_dl_runtime_resolve_slow FEATURE_INDEX_1*FEATURE_SIZE
+# define index_arch_Prefer_No_AVX512	FEATURE_INDEX_1*FEATURE_SIZE
 
 
 # if defined (_LIBC) && !IS_IN (nonlib)
@@ -302,6 +304,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 # define index_arch_Prefer_ERMS		FEATURE_INDEX_1
 # define index_arch_Use_dl_runtime_resolve_opt FEATURE_INDEX_1
 # define index_arch_Use_dl_runtime_resolve_slow FEATURE_INDEX_1
+# define index_arch_Prefer_No_AVX512	FEATURE_INDEX_1
 
 #endif	/* !__ASSEMBLER__ */