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Message-Id: <40e2700f8cda4d511e5910be1e633025d28b36c2.1306156808.git.luto@mit.edu>
Date: Mon, 23 May 2011 09:31:31 -0400
From: Andy Lutomirski <luto@....EDU>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andi Kleen <andi@...stfloor.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <eric.dumazet@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...64.org>, Andy Lutomirski <luto@....edu>
Subject: [PATCH v5 8/8] x86-64: Optimize vDSO time()
This function just reads a 64-bit variable that's updated
atomically, so we don't need any locks.
Signed-off-by: Andy Lutomirski <luto@....edu>
---
arch/x86/vdso/vclock_gettime.c | 8 ++------
1 files changed, 2 insertions(+), 6 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index e6e9f90..a69929e 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -180,12 +180,8 @@ notrace time_t __vdso_time(time_t *t)
if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
return time_syscall(t);
- do {
- seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
-
- result = VVAR(vsyscall_gtod_data).wall_time_sec;
-
- } while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
+ /* This is atomic on x86_64 so we don't need any locks. */
+ result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
if (t)
*t = result;
--
1.7.5.1
--
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