Aren/NetBSD
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

For this case during build.sh:

Browse Source 
rw_enter(lock, RW_READ);

Having instrumented it, it turns out that >99.5% of the time the lock is
completely unknowned.  Make this assumption in the assembly stub for
rw_enter(), and avoid the initial read of the lock word.  Where there are
existing read holds, we'll do an additional CMPXCHG but should already have
the cache line in the EXCLUSIVE state.
This commit is contained in:
ad 2019-11-23 16:36:38 +00:00
parent b5c5b66961
commit 27c7e48ae9
2 changed files with 23 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
sys/arch/amd64/amd64/lock_stubs.S
View File

@ -1,4 +1,4 @@
/* $NetBSD: lock_stubs.S,v 1.33 2019/11/14 16:23:52 maxv Exp $ */
/* $NetBSD: lock_stubs.S,v 1.34 2019/11/23 16:36:38 ad Exp $ */
/*
* Copyright (c) 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
@ -191,13 +191,15 @@ END(mutex_spin_exit)
* Acquire one hold on a RW lock.
*/
ENTRY(rw_enter)
cmpl $RW_READER, %esi
xorl %eax, %eax
testl %esi, %esi /* RW_READER = 0 */
jne 2f
/*
* Reader: this is the most common case.
* Reader, and no existing readers on the lock: this is a most
* common case. Instead of reading from the lock word, use cmpxchg
* and get the cache line into the EXCLUSIVE state to begin with.
*/
movq (%rdi), %rax
0:
testb $(RW_WRITE_LOCKED|RW_WRITE_WANTED), %al
jnz 3f
@ -213,7 +215,6 @@ ENTRY(rw_enter)
* Writer: if the compare-and-set fails, don't bother retrying.
*/
2: movq CPUVAR(CURLWP), %rcx
xorq %rax, %rax
orq $RW_WRITE_LOCKED, %rcx
LOCK
cmpxchgq %rcx, (%rdi)
@ -268,13 +269,15 @@ END(rw_exit)
* Try to acquire one hold on a RW lock.
*/
ENTRY(rw_tryenter)
cmpl $RW_READER, %esi
xorl %eax, %eax
testl %esi, %esi /* RW_READER = 0 */
jne 2f
/*
* Reader: this is the most common case.
* Reader, and no existing readers on the lock: this is a most
* common case. Instead of reading from the lock word, use cmpxchg
* and get the cache line into the EXCLUSIVE state to begin with.
*/
movq (%rdi), %rax
0:
testb $(RW_WRITE_LOCKED|RW_WRITE_WANTED), %al
jnz 4f
@ -291,7 +294,6 @@ ENTRY(rw_tryenter)
* Writer: if the compare-and-set fails, don't bother retrying.
*/
2: movq CPUVAR(CURLWP), %rcx
xorq %rax, %rax
orq $RW_WRITE_LOCKED, %rcx
LOCK
cmpxchgq %rcx, (%rdi)

21
sys/arch/i386/i386/lock_stubs.S
View File

@ -1,7 +1,7 @@
/* $NetBSD: lock_stubs.S,v 1.30 2019/02/11 14:59:32 cherry Exp $ */
/* $NetBSD: lock_stubs.S,v 1.31 2019/11/23 16:36:38 ad Exp $ */
/*-
* Copyright (c) 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
* Copyright (c) 2006, 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
@ -35,7 +35,7 @@
*/
#include <machine/asm.h>
__KERNEL_RCSID(0, "$NetBSD: lock_stubs.S,v 1.30 2019/02/11 14:59:32 cherry Exp $");
__KERNEL_RCSID(0, "$NetBSD: lock_stubs.S,v 1.31 2019/11/23 16:36:38 ad Exp $");
#include "opt_lockdebug.h"
@ -104,13 +104,15 @@ END(mutex_exit)
*/
ENTRY(rw_enter)
movl 4(%esp), %edx
xorl %eax, %eax
cmpl $RW_READER, 8(%esp)
jne 2f
/*
* Reader
* Reader, and no existing readers on the lock: this is a most
* common case. Instead of reading from the lock word, use cmpxchg
* and get the cache line into the EXCLUSIVE state to begin with.
*/
movl (%edx), %eax
0:
testb $(RW_WRITE_LOCKED|RW_WRITE_WANTED), %al
jnz 3f
@ -125,7 +127,7 @@ ENTRY(rw_enter)
/*
* Writer
*/
2: xorl %eax, %eax
2:
movl %fs:CPU_INFO_CURLWP(%eax), %ecx
orl $RW_WRITE_LOCKED, %ecx
LOCK(3)
@ -186,13 +188,15 @@ END(rw_exit)
*/
ENTRY(rw_tryenter)
movl 4(%esp), %edx
xorl %eax, %eax
cmpl $RW_READER, 8(%esp)
jne 2f
/*
* Reader
* Reader, and no existing readers on the lock: this is a most
* common case. Instead of reading from the lock word, use cmpxchg
* and get the cache line into the EXCLUSIVE state to begin with.
*/
movl (%edx), %eax
0:
testb $(RW_WRITE_LOCKED|RW_WRITE_WANTED), %al
jnz 4f
@ -209,7 +213,6 @@ ENTRY(rw_tryenter)
* Writer
*/
2:
xorl %eax, %eax
movl %fs:CPU_INFO_CURLWP(%eax), %ecx
orl $RW_WRITE_LOCKED, %ecx
LOCK(13)