When AP firstly wakes up, MpFuncs.nasm contains below logic to assign
an unique ApIndex to each AP according to who comes first:
---NASM---
mov edi, esi
add edi, MP_CPU_EXCHANGE_INFO_FIELD (Lock)
mov eax, NotVacantFlag
TestLock:
xchg [edi], eax
cmp eax, NotVacantFlag
jz TestLock
mov ecx, esi
add ecx, MP_CPU_EXCHANGE_INFO_FIELD (ApIndex)
inc dword [ecx]
mov ebx, [ecx]
Releaselock:
mov eax, VacantFlag
xchg [edi], eax
---NASM END---
"LOCK INC" cannot be used to increase MP_CPU_EXCHANGE_INFO.ApIndex
because not only the MP_CPU_EXCHANGE_INFO.ApIndex should be
increased, but also the result should be stored to a thread 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: Laszlo Ersek <ler...@redhat.com>
Cc: Eric Dong <eric.d...@intel.com>
Cc: Rahul1 Kumar <rahul1.ku...@intel.com>
---
.../Library/MpInitLib/Ia32/MpFuncs.nasm | 20 ++++---------------
UefiCpuPkg/Library/MpInitLib/MpEqu.inc | 4 ----
UefiCpuPkg/Library/MpInitLib/MpLib.c | 1 -
UefiCpuPkg/Library/MpInitLib/MpLib.h | 3 +--
UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm | 18 ++++-------------
5 files changed, 9 insertions(+), 37 deletions(-)
diff --git a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
index 2f1b102717..7bd2415670 100644
--- a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
@@ -122,22 +122,10 @@ SkipEnableExecuteDisable:
; AP init
mov edi, esi
- add edi, MP_CPU_EXCHANGE_INFO_FIELD (Lock)
- mov eax, NotVacantFlag
-
-TestLock:
- xchg [edi], eax
- cmp eax, NotVacantFlag
- jz TestLock
-
- mov ecx, esi
- add ecx, MP_CPU_EXCHANGE_INFO_FIELD (ApIndex)
- inc dword [ecx]
- mov ebx, [ecx]
-
-Releaselock:
- mov eax, VacantFlag
- xchg [edi], eax
+ add edi, MP_CPU_EXCHANGE_INFO_FIELD (ApIndex)
+ mov ebx, 1
+ lock xadd dword [edi], ebx ; EBX = ApIndex++
+ inc ebx ; EBX is CpuNumber
mov edi, esi
add edi, MP_CPU_EXCHANGE_INFO_FIELD (StackSize)
diff --git a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
index 46c2b5c116..2e9368a374 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
+++ b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
@@ -13,9 +13,6 @@
;-------------------------------------------------------------------------------
%include "Nasm.inc"
-VacantFlag equ 00h
-NotVacantFlag equ 0ffh
-
CPU_SWITCH_STATE_IDLE equ 0
CPU_SWITCH_STATE_STORED equ 1
CPU_SWITCH_STATE_LOADED equ 2
@@ -72,7 +69,6 @@ endstruc
; Equivalent NASM structure of MP_CPU_EXCHANGE_INFO
;
struc MP_CPU_EXCHANGE_INFO
- .Lock: CTYPE_UINTN 1
.StackStart: CTYPE_UINTN 1
.StackSize: CTYPE_UINTN 1
.CFunction: CTYPE_UINTN 1
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c
b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 2568986d8c..5040053dad 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1006,7 +1006,6 @@ FillExchangeInfoData (
IA32_CR4 Cr4;
ExchangeInfo = CpuMpData->MpCpuExchangeInfo;
- ExchangeInfo->Lock = 0;
ExchangeInfo->StackStart = CpuMpData->Buffer;
ExchangeInfo->StackSize = CpuMpData->CpuApStackSize;
ExchangeInfo->BufferStart = CpuMpData->WakeupBuffer;
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h
b/UefiCpuPkg/Library/MpInitLib/MpLib.h
index 02652eaae1..0bd60388b1 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
@@ -1,7 +1,7 @@
/** @file
Common header file for MP Initialize Library.
- Copyright (c) 2016 - 2020, Intel Corporation. All rights reserved.<BR>
+ Copyright (c) 2016 - 2021, Intel Corporation. All rights reserved.<BR>
Copyright (c) 2020, AMD Inc. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
@@ -190,7 +190,6 @@ typedef struct _CPU_MP_DATA CPU_MP_DATA;
// into this structure are used in assembly code in this module
//
typedef struct {
- UINTN Lock;
UINTN StackStart;
UINTN StackSize;
UINTN CFunction;
diff --git a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
index bf7faaf60b..50df802d1f 100644
--- a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
@@ -158,21 +158,11 @@ LongModeStart:
; AP init
mov edi, esi
- add edi, MP_CPU_EXCHANGE_INFO_FIELD (Lock)
- mov rax, NotVacantFlag
+ add edi, MP_CPU_EXCHANGE_INFO_FIELD (ApIndex)
+ mov ebx, 1
+ lock xadd dword [edi], ebx ; EBX = ApIndex++
+ inc ebx ; EBX is CpuNumber
-TestLock:
- xchg qword [edi], rax
- cmp rax, NotVacantFlag
- jz TestLock
-
- lea ecx, [esi + MP_CPU_EXCHANGE_INFO_FIELD (ApIndex)]
- inc dword [ecx]
- mov ebx, [ecx]
-
-Releaselock:
- mov rax, VacantFlag
- xchg qword [edi], rax
; program stack
mov edi, esi
add edi, MP_CPU_EXCHANGE_INFO_FIELD (StackSize)
--
2.27.0.windows.1
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