diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-09-25 16:55:48 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2023-10-09 18:14:25 +0200 |
| commit | 636d6a8b850a2bb8462b5f743c9db9aa4d735cda (patch) | |
| tree | 85a29ffed8d321ad77f49281632de74a45febd4e /arch/x86/include/asm/cmpxchg.h | |
| parent | e01cc1e8c2ad73cebb980878ede5584e0f2688f7 (diff) | |
locking/atomic/x86: Introduce arch_sync_try_cmpxchg()
Introduce the arch_sync_try_cmpxchg() macro to improve code using
sync_try_cmpxchg() locking primitive. The new definitions use existing
__raw_try_cmpxchg() macros, but use its own "lock; " prefix.
The new macros improve assembly of the cmpxchg loop in
evtchn_fifo_unmask() from drivers/xen/events/events_fifo.c from:
57a: 85 c0 test %eax,%eax
57c: 78 52 js 5d0 <...>
57e: 89 c1 mov %eax,%ecx
580: 25 ff ff ff af and $0xafffffff,%eax
585: c7 04 24 00 00 00 00 movl $0x0,(%rsp)
58c: 81 e1 ff ff ff ef and $0xefffffff,%ecx
592: 89 4c 24 04 mov %ecx,0x4(%rsp)
596: 89 44 24 08 mov %eax,0x8(%rsp)
59a: 8b 74 24 08 mov 0x8(%rsp),%esi
59e: 8b 44 24 04 mov 0x4(%rsp),%eax
5a2: f0 0f b1 32 lock cmpxchg %esi,(%rdx)
5a6: 89 04 24 mov %eax,(%rsp)
5a9: 8b 04 24 mov (%rsp),%eax
5ac: 39 c1 cmp %eax,%ecx
5ae: 74 07 je 5b7 <...>
5b0: a9 00 00 00 40 test $0x40000000,%eax
5b5: 75 c3 jne 57a <...>
<...>
to:
578: a9 00 00 00 40 test $0x40000000,%eax
57d: 74 2b je 5aa <...>
57f: 85 c0 test %eax,%eax
581: 78 40 js 5c3 <...>
583: 89 c1 mov %eax,%ecx
585: 25 ff ff ff af and $0xafffffff,%eax
58a: 81 e1 ff ff ff ef and $0xefffffff,%ecx
590: 89 4c 24 04 mov %ecx,0x4(%rsp)
594: 89 44 24 08 mov %eax,0x8(%rsp)
598: 8b 4c 24 08 mov 0x8(%rsp),%ecx
59c: 8b 44 24 04 mov 0x4(%rsp),%eax
5a0: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
5a4: 89 44 24 04 mov %eax,0x4(%rsp)
5a8: 75 30 jne 5da <...>
<...>
5da: 8b 44 24 04 mov 0x4(%rsp),%eax
5de: eb 98 jmp 578 <...>
The new code removes move instructions from 585: 5a6: and 5a9:
and the compare from 5ac:. Additionally, the compiler assumes that
cmpxchg success is more probable and optimizes code flow accordingly.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Diffstat (limited to 'arch/x86/include/asm/cmpxchg.h')
| -rw-r--r-- | arch/x86/include/asm/cmpxchg.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h index d53636506134..5612648b0202 100644 --- a/arch/x86/include/asm/cmpxchg.h +++ b/arch/x86/include/asm/cmpxchg.h @@ -221,12 +221,18 @@ extern void __add_wrong_size(void) #define __try_cmpxchg(ptr, pold, new, size) \ __raw_try_cmpxchg((ptr), (pold), (new), (size), LOCK_PREFIX) +#define __sync_try_cmpxchg(ptr, pold, new, size) \ + __raw_try_cmpxchg((ptr), (pold), (new), (size), "lock; ") + #define __try_cmpxchg_local(ptr, pold, new, size) \ __raw_try_cmpxchg((ptr), (pold), (new), (size), "") #define arch_try_cmpxchg(ptr, pold, new) \ __try_cmpxchg((ptr), (pold), (new), sizeof(*(ptr))) +#define arch_sync_try_cmpxchg(ptr, pold, new) \ + __sync_try_cmpxchg((ptr), (pold), (new), sizeof(*(ptr))) + #define arch_try_cmpxchg_local(ptr, pold, new) \ __try_cmpxchg_local((ptr), (pold), (new), sizeof(*(ptr))) |