From 973aa8181e10050809b56ecbaadd01495766a19e Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Mon, 23 May 2011 09:31:31 -0400 Subject: [PATCH] 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 Cc: Andi Kleen Cc: Linus Torvalds Cc: "David S. Miller" Cc: Eric Dumazet Cc: Peter Zijlstra Cc: Borislav Petkov Link: http://lkml.kernel.org/r/%3C40e2700f8cda4d511e5910be1e633025d28b36c2.1306156808.git.luto%40mit.edu%3E Signed-off-by: Thomas Gleixner --- arch/x86/vdso/vclock_gettime.c | 8 ++------ 1 file 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; -- 2.7.4