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authorAndy Lutomirski <luto@MIT.EDU>2011-05-23 09:31:31 -0400
committerThomas Gleixner <tglx@linutronix.de>2011-05-24 14:51:29 +0200
commit973aa8181e10050809b56ecbaadd01495766a19e (patch)
tree0ca3fa4159ab439913a26bba412db5cbbe1737eb
parentf144a6b4d1688675d88990e29567b2335b48205e (diff)
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@mit.edu> Cc: Andi Kleen <andi@firstfloor.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Borislav Petkov <bp@amd64.org> Link: http://lkml.kernel.org/r/%3C40e2700f8cda4d511e5910be1e633025d28b36c2.1306156808.git.luto%40mit.edu%3E Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--arch/x86/vdso/vclock_gettime.c8
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index e6e9f90a8cd7..a69929e8bfdb 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;