[PATCH v5 8/8] x86-64: Optimize vDSO time()

[Andy Lutomirski <luto@MIT.EDU>]

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>
---
 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