X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
Commit Message
There is transition penalty when SSE instructions are mixed with 256-bit
AVX or 512-bit AVX512 load instructions. Since _dl_runtime_resolve_avx
and _dl_runtime_profile_avx512 save/restore 256-bit YMM/512-bit ZMM
registers, there is transition penalty when SSE instructions are used
with lazy binding on AVX and AVX512 processors.
For AVX and AVX512 processors which support XGETBV with ECX == 1, we can
use XGETBV with ECX == 1 to check if the upper 128 bits of YMM registers
or the upper 256 bits of ZMM registers are zero. We can restore only the
non-zero portion of vector registers with AVX/AVX512 load instructions
which will zero-extend upper bits of vector registers.
This patch adds _dl_runtime_resolve_sse_vex which saves and restores
XMM registers with 128-bit AVX store/load instructions. It is used to
preserve YMM/ZMM registers when only the lower 128 bits are non-zero.
_dl_runtime_resolve_avx_opt and _dl_runtime_resolve_avx512_opt are added
and used on AVX/AVX512 processors supporting XGETBV with ECX == 1 so
that we store and load only the non-zero portion of vector registers.
This avoids SSE transition penalty caused by _dl_runtime_resolve_avx and
_dl_runtime_profile_avx512 when only the lower 128 bits of vector
registers are used.
Tested on x86-64 with/without AVX/AVX512. OK for master?
[BZ #20508]
* sysdeps/x86/cpu-features.c (init_cpu_features): Set
Use_dl_runtime_resolve_opt if XGETBV suports ECX == 1.
* sysdeps/x86/cpu-features.h (bit_arch_Use_dl_runtime_resolve_opt):
New.
(index_arch_Use_dl_runtime_resolve_opt): Likewise.
* sysdeps/x86_64/dl-machine.h (elf_machine_runtime_setup): Use
_dl_runtime_resolve_avx512_opt and _dl_runtime_resolve_avx_opt
if Use_dl_runtime_resolve_opt is set.
* sysdeps/x86_64/dl-trampoline.S: Include <cpu-features.h>.
(_dl_runtime_resolve_opt): New. Defined for AVX and AVX512.
(_dl_runtime_resolve): Add one for _dl_runtime_resolve_sse_vex.
* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve_opt): New.
(_dl_runtime_profile): Define only if _dl_runtime_profile is
defined.
Comments
On 08/23/2016 11:53 PM, H.J. Lu wrote:
> Tested on x86-64 with/without AVX/AVX512. OK for master?
Is this supposed to address a performance issue in actually shipping
silicon?
It seems there are implementations out there which support AVX-512F and
XSAVEOPT, but not the XGETBV functionality required by this patch.
Florian
On Wed, Aug 24, 2016 at 3:55 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 08/23/2016 11:53 PM, H.J. Lu wrote:
>>
>> Tested on x86-64 with/without AVX/AVX512. OK for master?
>
>
> Is this supposed to address a performance issue in actually shipping
> silicon?
We only see this performance issue with SSE AES instructions on
AVX512 machines with XGETBV (ECX == 1) and my patch fixes it.
Other AVX machines and other SSE instructions are OK.
> It seems there are implementations out there which support AVX-512F and
> XSAVEOPT, but not the XGETBV functionality required by this patch.
Knights Landing doesn't have this performance issue.
From d963b835c1e0fe430a88168a81c4c69dcd9ad00c Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 23 Aug 2016 09:09:32 -0700
Subject: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]
There is transition penalty when SSE instructions are mixed with 256-bit
AVX or 512-bit AVX512 load instructions. Since _dl_runtime_resolve_avx
and _dl_runtime_profile_avx512 save/restore 256-bit YMM/512-bit ZMM
registers, there is transition penalty when SSE instructions are used
with lazy binding on AVX and AVX512 processors.
For AVX and AVX512 processors which support XGETBV with ECX == 1, we can
use XGETBV with ECX == 1 to check if the upper 128 bits of YMM registers
or the upper 256 bits of ZMM registers are zero. We can restore only the
non-zero portion of vector registers with AVX/AVX512 load instructions
which will zero-extend upper bits of vector registers.
This patch adds _dl_runtime_resolve_sse_vex which saves and restores
XMM registers with 128-bit AVX store/load instructions. It is used to
preserve YMM/ZMM registers when only the lower 128 bits are non-zero.
_dl_runtime_resolve_avx_opt and _dl_runtime_resolve_avx512_opt are added
and used on AVX/AVX512 processors supporting XGETBV with ECX == 1 so
that we store and load only the non-zero portion of vector registers.
This avoids SSE transition penalty caused by _dl_runtime_resolve_avx and
_dl_runtime_profile_avx512 when only the lower 128 bits of vector
registers are used.
[BZ #20508]
* sysdeps/x86/cpu-features.c (init_cpu_features): Set
Use_dl_runtime_resolve_opt if XGETBV suports ECX == 1.
* sysdeps/x86/cpu-features.h (bit_arch_Use_dl_runtime_resolve_opt):
New.
(index_arch_Use_dl_runtime_resolve_opt): Likewise.
* sysdeps/x86_64/dl-machine.h (elf_machine_runtime_setup): Use
_dl_runtime_resolve_avx512_opt and _dl_runtime_resolve_avx_opt
if Use_dl_runtime_resolve_opt is set.
* sysdeps/x86_64/dl-trampoline.S: Include <cpu-features.h>.
(_dl_runtime_resolve_opt): New. Defined for AVX and AVX512.
(_dl_runtime_resolve): Add one for _dl_runtime_resolve_sse_vex.
* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve_opt): New.
(_dl_runtime_profile): Define only if _dl_runtime_profile is
defined.
---
sysdeps/x86/cpu-features.c | 11 ++++++++
sysdeps/x86/cpu-features.h | 3 +++
sysdeps/x86_64/dl-machine.h | 20 ++++++++++++--
sysdeps/x86_64/dl-trampoline.S | 20 ++++++++++++++
sysdeps/x86_64/dl-trampoline.h | 60 +++++++++++++++++++++++++++++++++++++++++-
5 files changed, 111 insertions(+), 3 deletions(-)
@@ -205,6 +205,17 @@ init_cpu_features (struct cpu_features *cpu_features)
if (CPU_FEATURES_ARCH_P (cpu_features, AVX2_Usable))
cpu_features->feature[index_arch_AVX_Fast_Unaligned_Load]
|= bit_arch_AVX_Fast_Unaligned_Load;
+
+ if (cpu_features->max_cpuid >= 0xd)
+ {
+ unsigned int eax;
+
+ __cpuid_count (0xd, 1, eax, ebx, ecx, edx);
+ /* Use _dl_runtime_resolve_opt if XGETBV suports ECX == 1. */
+ if ((eax & (1 << 2)) != 0)
+ cpu_features->feature[index_arch_Use_dl_runtime_resolve_opt]
+ |= bit_arch_Use_dl_runtime_resolve_opt;
+ }
}
/* This spells out "AuthenticAMD". */
else if (ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65)
@@ -37,6 +37,7 @@
#define bit_arch_Prefer_No_VZEROUPPER (1 << 17)
#define bit_arch_Fast_Unaligned_Copy (1 << 18)
#define bit_arch_Prefer_ERMS (1 << 19)
+#define bit_arch_Use_dl_runtime_resolve_opt (1 << 20)
/* CPUID Feature flags. */
@@ -107,6 +108,7 @@
# define index_arch_Prefer_No_VZEROUPPER FEATURE_INDEX_1*FEATURE_SIZE
# define index_arch_Fast_Unaligned_Copy FEATURE_INDEX_1*FEATURE_SIZE
# define index_arch_Prefer_ERMS FEATURE_INDEX_1*FEATURE_SIZE
+# define index_arch_Use_dl_runtime_resolve_opt FEATURE_INDEX_1*FEATURE_SIZE
# if defined (_LIBC) && !IS_IN (nonlib)
@@ -277,6 +279,7 @@ extern const struct cpu_features *__get_cpu_features (void)
# define index_arch_Prefer_No_VZEROUPPER FEATURE_INDEX_1
# define index_arch_Fast_Unaligned_Copy FEATURE_INDEX_1
# define index_arch_Prefer_ERMS FEATURE_INDEX_1
+# define index_arch_Use_dl_runtime_resolve_opt FEATURE_INDEX_1
#endif /* !__ASSEMBLER__ */
@@ -68,7 +68,9 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
Elf64_Addr *got;
extern void _dl_runtime_resolve_sse (ElfW(Word)) attribute_hidden;
extern void _dl_runtime_resolve_avx (ElfW(Word)) attribute_hidden;
+ extern void _dl_runtime_resolve_avx_opt (ElfW(Word)) attribute_hidden;
extern void _dl_runtime_resolve_avx512 (ElfW(Word)) attribute_hidden;
+ extern void _dl_runtime_resolve_avx512_opt (ElfW(Word)) attribute_hidden;
extern void _dl_runtime_profile_sse (ElfW(Word)) attribute_hidden;
extern void _dl_runtime_profile_avx (ElfW(Word)) attribute_hidden;
extern void _dl_runtime_profile_avx512 (ElfW(Word)) attribute_hidden;
@@ -118,9 +120,23 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
indicated by the offset on the stack, and then jump to
the resolved address. */
if (HAS_ARCH_FEATURE (AVX512F_Usable))
- *(ElfW(Addr) *) (got + 2) = (ElfW(Addr)) &_dl_runtime_resolve_avx512;
+ {
+ if (HAS_ARCH_FEATURE (Use_dl_runtime_resolve_opt))
+ *(ElfW(Addr) *) (got + 2)
+ = (ElfW(Addr)) &_dl_runtime_resolve_avx512_opt;
+ else
+ *(ElfW(Addr) *) (got + 2)
+ = (ElfW(Addr)) &_dl_runtime_resolve_avx512;
+ }
else if (HAS_ARCH_FEATURE (AVX_Usable))
- *(ElfW(Addr) *) (got + 2) = (ElfW(Addr)) &_dl_runtime_resolve_avx;
+ {
+ if (HAS_ARCH_FEATURE (Use_dl_runtime_resolve_opt))
+ *(ElfW(Addr) *) (got + 2)
+ = (ElfW(Addr)) &_dl_runtime_resolve_avx_opt;
+ else
+ *(ElfW(Addr) *) (got + 2)
+ = (ElfW(Addr)) &_dl_runtime_resolve_avx;
+ }
else
*(ElfW(Addr) *) (got + 2) = (ElfW(Addr)) &_dl_runtime_resolve_sse;
}
@@ -18,6 +18,7 @@
#include <config.h>
#include <sysdep.h>
+#include <cpu-features.h>
#include <link-defines.h>
#ifndef DL_STACK_ALIGNMENT
@@ -86,9 +87,11 @@
#endif
#define VEC(i) zmm##i
#define _dl_runtime_resolve _dl_runtime_resolve_avx512
+#define _dl_runtime_resolve_opt _dl_runtime_resolve_avx512_opt
#define _dl_runtime_profile _dl_runtime_profile_avx512
#include "dl-trampoline.h"
#undef _dl_runtime_resolve
+#undef _dl_runtime_resolve_opt
#undef _dl_runtime_profile
#undef VEC
#undef VMOV
@@ -104,9 +107,11 @@
#endif
#define VEC(i) ymm##i
#define _dl_runtime_resolve _dl_runtime_resolve_avx
+#define _dl_runtime_resolve_opt _dl_runtime_resolve_avx_opt
#define _dl_runtime_profile _dl_runtime_profile_avx
#include "dl-trampoline.h"
#undef _dl_runtime_resolve
+#undef _dl_runtime_resolve_opt
#undef _dl_runtime_profile
#undef VEC
#undef VMOV
@@ -126,3 +131,18 @@
#define _dl_runtime_profile _dl_runtime_profile_sse
#undef RESTORE_AVX
#include "dl-trampoline.h"
+#undef _dl_runtime_resolve
+#undef _dl_runtime_profile
+#undef VMOV
+#undef VMOVA
+
+/* Used by _dl_runtime_resolve_avx_opt/_dl_runtime_resolve_avx512_opt
+ to preserve the full vector registers with zero upper bits. */
+#define VMOVA vmovdqa
+#if DL_RUNTIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT
+# define VMOV vmovdqa
+#else
+# define VMOV vmovdqu
+#endif
+#define _dl_runtime_resolve _dl_runtime_resolve_sse_vex
+#include "dl-trampoline.h"
@@ -50,6 +50,61 @@
#endif
.text
+#ifdef _dl_runtime_resolve_opt
+/* Use the smallest vector registers to preserve the full YMM/ZMM
+ registers to avoid SSE transition penalty. */
+ .globl _dl_runtime_resolve_opt
+ .hidden _dl_runtime_resolve_opt
+ .type _dl_runtime_resolve_opt, @function
+ .align 16
+_dl_runtime_resolve_opt:
+ cfi_startproc
+ cfi_adjust_cfa_offset(16) # Incorporate PLT
+ pushq %rax
+ cfi_adjust_cfa_offset(8)
+ cfi_rel_offset(%rax, 0)
+ pushq %rcx
+ cfi_adjust_cfa_offset(8)
+ cfi_rel_offset(%rcx, 0)
+ pushq %rdx
+ cfi_adjust_cfa_offset(8)
+ cfi_rel_offset(%rdx, 0)
+ movl $1, %ecx
+ xgetbv
+ movl %eax, %r11d
+ popq %rdx
+ cfi_adjust_cfa_offset(-8)
+ cfi_restore (%rdx)
+ popq %rcx
+ cfi_adjust_cfa_offset(-8)
+ cfi_restore (%rcx)
+ popq %rax
+ cfi_adjust_cfa_offset(-8)
+ cfi_restore (%rax)
+# if VEC_SIZE == 32
+ # For YMM registers, check if YMM state is in use.
+ andl $bit_YMM_state, %r11d
+ # Only preserve %xmm0 - %xmm7 registers with zero upper bits if
+ # YMM state isn't in use.
+ jz _dl_runtime_resolve_sse_vex
+# elif VEC_SIZE == 64
+ # For ZMM registers, check if YMM state and ZMM state are in
+ # use.
+ andl $(bit_YMM_state | bit_ZMM0_15_state), %r11d
+ cmpl $bit_YMM_state, %r11d
+ # Only preserve %xmm0 - %xmm7 registers with zero upper bits if
+ # neither YMM state nor ZMM state are in use.
+ jl _dl_runtime_resolve_sse_vex
+ # Only preserve %ymm0 - %ymm7 registers with zero upper bits if
+ # ZMM state isn't in use.
+ je _dl_runtime_resolve_avx
+# else
+# error Unsupported VEC_SIZE!
+# endif
+ cfi_adjust_cfa_offset(-16) # Restore PLT adjustment
+ cfi_endproc
+ .size _dl_runtime_resolve_opt, .-_dl_runtime_resolve_opt
+#endif
.globl _dl_runtime_resolve
.hidden _dl_runtime_resolve
.type _dl_runtime_resolve, @function
@@ -164,7 +219,10 @@ _dl_runtime_resolve:
.size _dl_runtime_resolve, .-_dl_runtime_resolve
-#ifndef PROF
+/* To preserve %xmm0 - %xmm7 registers, dl-trampoline.h is included
+ twice, for _dl_runtime_resolve_sse and _dl_runtime_resolve_sse_vex.
+ But we don't need another _dl_runtime_profile for XMM registers. */
+#if !defined PROF && defined _dl_runtime_profile
# if (LR_VECTOR_OFFSET % VEC_SIZE) != 0
# error LR_VECTOR_OFFSET must be multples of VEC_SIZE
# endif
--
2.7.4