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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>
This commit is contained in:
Andy Lutomirski 2012-03-22 21:15:51 -07:00 committed by John Stultz
parent 88b28adf6f
commit 91ec87d57f
3 changed files with 26 additions and 37 deletions
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15
arch/x86/include/asm/vgtod.h
View File

@ -7,11 +7,6 @@
struct vsyscall_gtod_data {
seqcount_t seq;
/* open coded 'struct timespec' */
time_t wall_time_sec;
u32 wall_time_nsec;
struct timezone sys_tz;
struct { /* extract of a clocksource struct */
int vclock_mode;
cycle_t cycle_last;
@ -19,8 +14,16 @@ struct vsyscall_gtod_data {
u32 mult;
u32 shift;
} clock;
struct timespec wall_to_monotonic;
/* open coded 'struct timespec' */
time_t wall_time_sec;
u32 wall_time_nsec;
u32 monotonic_time_nsec;
time_t monotonic_time_sec;
struct timezone sys_tz;
struct timespec wall_time_coarse;
struct timespec monotonic_time_coarse;
};
extern struct vsyscall_gtod_data vsyscall_gtod_data;

10
arch/x86/kernel/vsyscall_64.c
View File

@ -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);
}

38
arch/x86/vdso/vclock_gettime.c
View File

@ -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;
}