Reviewed-by: Eric Dong <eric.d...@intel.com>
-----Original Message-----
From: Ni, Ray <ray...@intel.com>
Sent: Tuesday, February 9, 2021 10:17 PM
To: devel@edk2.groups.io
Cc: Dong, Eric <eric.d...@intel.com>; Laszlo Ersek <ler...@redhat.com>; Kumar,
Rahul1 <rahul1.ku...@intel.com>
Subject: [PATCH v3 1/4] UefiCpuPkg/MpInitLib: Use XADD to avoid lock
acquire/release
When AP firstly wakes up, MpFuncs.nasm contains below logic to assign an unique
ApIndex to each AP according to who comes first:
---ASM---
TestLock:
xchg [edi], eax
cmp eax, NotVacantFlag
jz TestLock
mov ecx, esi
add ecx, ApIndexLocation
inc dword [ecx]
mov ebx, [ecx]
Releaselock:
mov eax, VacantFlag
xchg [edi], eax
---ASM END---
"lock inc" cannot be used to increase ApIndex because not only the global
ApIndex should be increased, but also the result should be stored to a local
general purpose register EBX.
This patch learns from the NASM implementation of
InternalSyncIncrement() to use "XADD" instruction which can increase the global
ApIndex and store the original ApIndex to EBX in one instruction.
With this patch, OVMF when running in a 255 threads QEMU spends about one
second to wakeup all APs. Original implementation needs more than
10 seconds.
Signed-off-by: Ray Ni <ray...@intel.com>
Cc: Eric Dong <eric.d...@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Rahul Kumar <rahul1.ku...@intel.com>
---
.../Library/MpInitLib/Ia32/MpFuncs.nasm | 20 ++++++-------------
UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm | 18 ++++++-----------
2 files changed, 12 insertions(+), 26 deletions(-)
diff --git a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
index 7e81d24aa6..2eaddc93bc 100644
--- a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
@@ -1,5 +1,5 @@
;------------------------------------------------------------------------------
;-; Copyright (c) 2015 - 2019, Intel Corporation. All rights reserved.<BR>+;
Copyright (c) 2015 - 2021, Intel Corporation. All rights reserved.<BR> ;
SPDX-License-Identifier: BSD-2-Clause-Patent ; ; Module Name:@@ -125,19 +125,11
@@ SkipEnableExecuteDisable:
add edi, LockLocation mov eax, NotVacantFlag -TestLock:-
xchg [edi], eax- cmp eax, NotVacantFlag- jz
TestLock-- mov ecx, esi- add ecx, ApIndexLocation- inc
dword [ecx]- mov ebx, [ecx]--Releaselock:- mov eax,
VacantFlag- xchg [edi], eax+ mov edi, esi+ add
edi, ApIndexLocation+ mov ebx, 1+ lock xadd dword [edi], ebx
; EBX = ApIndex+++ inc ebx ;
EBX is CpuNumber mov edi, esi add edi,
StackSizeLocationdiff --git a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
index aecfd07bc0..5b588f2dcb 100644
--- a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
@@ -1,5 +1,5 @@
;------------------------------------------------------------------------------
;-; Copyright (c) 2015 - 2019, Intel Corporation. All rights reserved.<BR>+;
Copyright (c) 2015 - 2021, Intel Corporation. All rights reserved.<BR> ;
SPDX-License-Identifier: BSD-2-Clause-Patent ; ; Module Name:@@ -161,18 +161,12
@@ LongModeStart:
add edi, LockLocation mov rax, NotVacantFlag -TestLock:-
xchg qword [edi], rax- cmp rax, NotVacantFlag- jz
TestLock-- lea ecx, [esi + ApIndexLocation]- inc dword
[ecx]- mov ebx, [ecx]+ mov edi, esi+ add edi,
ApIndexLocation+ mov ebx, 1+ lock xadd dword [edi], ebx
; EBX = ApIndex+++ inc ebx ; EBX
is CpuNumber -Releaselock:- mov rax, VacantFlag- xchg qword
[edi], rax ; program stack mov edi, esi add edi,
StackSizeLocation--
2.27.0.windows.1
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