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


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