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authorAndy Lutomirski <luto@mit.edu>2012-03-22 21:15:51 -0700
committerJohn Stultz <john.stultz@linaro.org>2012-03-23 16:49:33 -0700
commit91ec87d57fc38c529034e853687dfb7756de5406 (patch)
tree4f88d6a7e0221bdd791a1de6d4c36b17da8337a2 /arch/x86/vdso
parent88b28adf6fcdd6d10a1cfc7765bb200d7366a265 (diff)
downloadop-kernel-dev-91ec87d57fc38c529034e853687dfb7756de5406.zip
op-kernel-dev-91ec87d57fc38c529034e853687dfb7756de5406.tar.gz
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>
Diffstat (limited to 'arch/x86/vdso')
-rw-r--r--arch/x86/vdso/vclock_gettime.c38
1 files changed, 8 insertions, 30 deletions
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 944c5e5..6eea70b8 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -113,27 +113,17 @@ notrace static noinline int do_realtime(struct timespec *ts)
notrace static noinline int do_monotonic(struct timespec *ts)
{
- unsigned long seq, ns, secs;
+ unsigned long seq, ns;
int mode;
do {
seq = read_seqcount_begin(&gtod->seq);
mode = gtod->clock.vclock_mode;
- secs = gtod->wall_time_sec;
- ns = gtod->wall_time_nsec + vgetns();
- secs += gtod->wall_to_monotonic.tv_sec;
- ns += gtod->wall_to_monotonic.tv_nsec;
+ ts->tv_sec = gtod->monotonic_time_sec;
+ ts->tv_nsec = gtod->monotonic_time_nsec;
+ ns = vgetns();
} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
-
- /* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
- * are all guaranteed to be nonnegative.
- */
- while (ns >= NSEC_PER_SEC) {
- ns -= NSEC_PER_SEC;
- ++secs;
- }
- ts->tv_sec = secs;
- ts->tv_nsec = ns;
+ timespec_add_ns(ts, ns);
return mode;
}
@@ -151,25 +141,13 @@ notrace static noinline int do_realtime_coarse(struct timespec *ts)
notrace static noinline int do_monotonic_coarse(struct timespec *ts)
{
- unsigned long seq, ns, secs;
+ unsigned long seq;
do {
seq = read_seqcount_begin(&gtod->seq);
- secs = gtod->wall_time_coarse.tv_sec;
- ns = gtod->wall_time_coarse.tv_nsec;
- secs += gtod->wall_to_monotonic.tv_sec;
- ns += gtod->wall_to_monotonic.tv_nsec;
+ ts->tv_sec = gtod->monotonic_time_coarse.tv_sec;
+ ts->tv_nsec = gtod->monotonic_time_coarse.tv_nsec;
} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
- /* wall_time_nsec and wall_to_monotonic.tv_nsec are
- * guaranteed to be between 0 and NSEC_PER_SEC.
- */
- if (ns >= NSEC_PER_SEC) {
- ns -= NSEC_PER_SEC;
- ++secs;
- }
- ts->tv_sec = secs;
- ts->tv_nsec = ns;
-
return 0;
}
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