diff mbox

x86: Use AVX2 memcpy/memset on Skylake server [BZ #21396]

Message ID 20170418183712.GA22211@intel.com
State New, archived
Headers

Commit Message

Lu, Hongjiu April 18, 2017, 6:37 p.m. UTC 
  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.

Any comments?


H.J.
---
	[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.
---
 sysdeps/x86/cpu-features.c             | 6 +++++-
 sysdeps/x86/cpu-features.h             | 3 +++
 sysdeps/x86_64/multiarch/memcpy.S      | 2 ++
 sysdeps/x86_64/multiarch/memcpy_chk.S  | 2 ++
 sysdeps/x86_64/multiarch/memmove.S     | 2 ++
 sysdeps/x86_64/multiarch/memmove_chk.S | 2 ++
 sysdeps/x86_64/multiarch/mempcpy.S     | 2 ++
 sysdeps/x86_64/multiarch/mempcpy_chk.S | 2 ++
 sysdeps/x86_64/multiarch/memset.S      | 2 ++
 sysdeps/x86_64/multiarch/memset_chk.S  | 2 ++
 10 files changed, 24 insertions(+), 1 deletion(-)

Comments

Florian Weimer April 18, 2017, 7:08 p.m. UTC | #1 
On 04/18/2017 08:37 PM, H.J. Lu wrote:
> 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 you bring this up: I think I have read reports that this happens 
with AVX2 and some parts, too.

The change itself looks reasonable.

Thanks,
Florian
H.J. Lu April 18, 2017, 7:21 p.m. UTC | #2 
On Tue, Apr 18, 2017 at 12:08 PM, Florian Weimer <fweimer@redhat.com> wrote:
> On 04/18/2017 08:37 PM, H.J. Lu wrote:
>>
>> 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 you bring this up: I think I have read reports that this happens with
> AVX2 and some parts, too.

That is true and AVX512 has higher impact on CPU frequency than AVX2.

> The change itself looks reasonable.
>
> Thanks,
> Florian
diff mbox

Patch

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index ae7f844..f30918d 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 1583d65..85a39e7 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__ */
 
diff --git a/sysdeps/x86_64/multiarch/memcpy.S b/sysdeps/x86_64/multiarch/memcpy.S
index 1f83ee3..af27703 100644
--- a/sysdeps/x86_64/multiarch/memcpy.S
+++ b/sysdeps/x86_64/multiarch/memcpy.S
@@ -32,6 +32,8 @@  ENTRY(__new_memcpy)
 	lea	__memcpy_erms(%rip), %RAX_LP
 	HAS_ARCH_FEATURE (Prefer_ERMS)
 	jnz	2f
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__memcpy_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/memcpy_chk.S b/sysdeps/x86_64/multiarch/memcpy_chk.S
index 5492342..8737fb9 100644
--- a/sysdeps/x86_64/multiarch/memcpy_chk.S
+++ b/sysdeps/x86_64/multiarch/memcpy_chk.S
@@ -30,6 +30,8 @@ 
 ENTRY(__memcpy_chk)
 	.type	__memcpy_chk, @gnu_indirect_function
 	LOAD_RTLD_GLOBAL_RO_RDX
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__memcpy_chk_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/memmove.S b/sysdeps/x86_64/multiarch/memmove.S
index 2021bfc..8c534e8 100644
--- a/sysdeps/x86_64/multiarch/memmove.S
+++ b/sysdeps/x86_64/multiarch/memmove.S
@@ -30,6 +30,8 @@  ENTRY(__libc_memmove)
 	lea	__memmove_erms(%rip), %RAX_LP
 	HAS_ARCH_FEATURE (Prefer_ERMS)
 	jnz	2f
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__memmove_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/memmove_chk.S b/sysdeps/x86_64/multiarch/memmove_chk.S
index 8a252ad..7870dd0 100644
--- a/sysdeps/x86_64/multiarch/memmove_chk.S
+++ b/sysdeps/x86_64/multiarch/memmove_chk.S
@@ -29,6 +29,8 @@ 
 ENTRY(__memmove_chk)
 	.type	__memmove_chk, @gnu_indirect_function
 	LOAD_RTLD_GLOBAL_RO_RDX
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__memmove_chk_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/mempcpy.S b/sysdeps/x86_64/multiarch/mempcpy.S
index 79c840d..b8b2b28 100644
--- a/sysdeps/x86_64/multiarch/mempcpy.S
+++ b/sysdeps/x86_64/multiarch/mempcpy.S
@@ -32,6 +32,8 @@  ENTRY(__mempcpy)
 	lea	__mempcpy_erms(%rip), %RAX_LP
 	HAS_ARCH_FEATURE (Prefer_ERMS)
 	jnz	2f
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__mempcpy_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/mempcpy_chk.S b/sysdeps/x86_64/multiarch/mempcpy_chk.S
index 6927962..072b22c 100644
--- a/sysdeps/x86_64/multiarch/mempcpy_chk.S
+++ b/sysdeps/x86_64/multiarch/mempcpy_chk.S
@@ -30,6 +30,8 @@ 
 ENTRY(__mempcpy_chk)
 	.type	__mempcpy_chk, @gnu_indirect_function
 	LOAD_RTLD_GLOBAL_RO_RDX
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	1f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	1f
 	lea	__mempcpy_chk_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/memset.S b/sysdeps/x86_64/multiarch/memset.S
index c958b2f..9d33118 100644
--- a/sysdeps/x86_64/multiarch/memset.S
+++ b/sysdeps/x86_64/multiarch/memset.S
@@ -41,6 +41,8 @@  ENTRY(memset)
 	jnz	L(AVX512F)
 	lea	__memset_avx2_unaligned(%rip), %RAX_LP
 L(AVX512F):
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	2f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	2f
 	lea	__memset_avx512_no_vzeroupper(%rip), %RAX_LP
diff --git a/sysdeps/x86_64/multiarch/memset_chk.S b/sysdeps/x86_64/multiarch/memset_chk.S
index 79eaa37..7e08311 100644
--- a/sysdeps/x86_64/multiarch/memset_chk.S
+++ b/sysdeps/x86_64/multiarch/memset_chk.S
@@ -38,6 +38,8 @@  ENTRY(__memset_chk)
 	jnz	L(AVX512F)
 	lea	__memset_chk_avx2_unaligned(%rip), %RAX_LP
 L(AVX512F):
+	HAS_ARCH_FEATURE (Prefer_No_AVX512)
+	jnz	2f
 	HAS_ARCH_FEATURE (AVX512F_Usable)
 	jz	2f
 	lea	__memset_chk_avx512_no_vzeroupper(%rip), %RAX_LP