x86-64: Simplify and optimize vdso clock_gettime monotonic variants

We used to store the wall-to-monotonic offset and the realtime base.
It's faster to precompute the monotonic base.

This is about a 3% speedup on Sandy Bridge for CLOCK_MONOTONIC.
It's much more impressive for CLOCK_MONOTONIC_COARSE.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index cdc95a707cd..4285f1f404c 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -84,6 +84,7 @@ void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
                         struct clocksource *clock, u32 mult)
 {
         write_seqcount_begin(&vsyscall_gtod_data.seq);
+        struct timespec monotonic;
 
         /* copy vsyscall data */
         vsyscall_gtod_data.clock.vclock_mode    = clock->archdata.vclock_mode;
@@ -91,10 +92,17 @@ void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
         vsyscall_gtod_data.clock.mask           = clock->mask;
         vsyscall_gtod_data.clock.mult           = mult;
         vsyscall_gtod_data.clock.shift          = clock->shift;
+
         vsyscall_gtod_data.wall_time_sec        = wall_time->tv_sec;
         vsyscall_gtod_data.wall_time_nsec       = wall_time->tv_nsec;
-        vsyscall_gtod_data.wall_to_monotonic    = *wtm;
+
+        monotonic = timespec_add(*wall_time, *wtm);
+        vsyscall_gtod_data.monotonic_time_sec   = monotonic.tv_sec;
+        vsyscall_gtod_data.monotonic_time_nsec  = monotonic.tv_nsec;
+
         vsyscall_gtod_data.wall_time_coarse     = __current_kernel_time();
+        vsyscall_gtod_data.monotonic_time_coarse =
+                timespec_add(vsyscall_gtod_data.wall_time_coarse, *wtm);
 
         write_seqcount_end(&vsyscall_gtod_data.seq);
 }