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Date: Sun, 25 Dec 2011 08:51:02 -0800
From: Andy Lutomirski <luto@...capital.net>
To: linux-kernel@...r.kernel.org, Kumar Sundararajan <kumar@...com>,
john stultz <johnstul@...ibm.com>, Arun Sharma <asharma@...com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>,
Richard Cochran <richardcochran@...il.com>,
Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 3/4] x86-64: Optimize vdso clock_gettime
This is a small improvement.
Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
arch/x86/include/asm/vgtod.h | 21 +++++++---
arch/x86/kernel/vsyscall_64.c | 25 +++++++++++-
arch/x86/vdso/vclock_gettime.c | 89 ++++++++++++++++++++++-----------------
3 files changed, 89 insertions(+), 46 deletions(-)
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 815285b..03b4999 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -7,11 +7,6 @@
struct vsyscall_gtod_data {
seqlock_t lock;
- /* 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 +14,22 @@ 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;
+
+ /* Flat counts for clock_ns_get */
+ u64 wall_time_flat_ns;
+ u64 monotonic_time_flat_ns;
+ u64 wall_time_coarse_flat_ns;
+ u64 monotonic_time_coarse_flat_ns;
+
+ struct timezone sys_tz;
struct timespec wall_time_coarse;
+ struct timespec monotonic_time_coarse;
};
extern struct vsyscall_gtod_data vsyscall_gtod_data;
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index b56c65de..9c2e148 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -91,6 +91,7 @@ void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
struct clocksource *clock, u32 mult)
{
unsigned long flags;
+ struct timespec monotonic;
write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
@@ -100,10 +101,32 @@ 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);
+
+ /* generate flat data for clock_ns_get */
+ vsyscall_gtod_data.wall_time_flat_ns =
+ vsyscall_gtod_data.wall_time_sec * NSEC_PER_SEC +
+ vsyscall_gtod_data.wall_time_nsec;
+ vsyscall_gtod_data.monotonic_time_flat_ns =
+ vsyscall_gtod_data.monotonic_time_sec * NSEC_PER_SEC +
+ vsyscall_gtod_data.monotonic_time_nsec;
+
+ vsyscall_gtod_data.wall_time_coarse_flat_ns =
+ vsyscall_gtod_data.wall_time_coarse.tv_sec * NSEC_PER_SEC +
+ vsyscall_gtod_data.wall_time_coarse.tv_nsec;
+ vsyscall_gtod_data.monotonic_time_coarse_flat_ns =
+ vsyscall_gtod_data.monotonic_time_coarse.tv_sec * NSEC_PER_SEC +
+ vsyscall_gtod_data.monotonic_time_coarse.tv_nsec;
write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index c8a2b46..fe960ac 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -94,26 +94,36 @@ notrace static noinline void do_realtime(struct timespec *ts)
timespec_add_ns(ts, ns);
}
+notrace static noinline u64 do_realtime_ns(void)
+{
+ unsigned long seq, ns;
+ do {
+ seq = read_seqbegin(>od->lock);
+ ns = gtod->wall_time_flat_ns + vgetns();
+ } while (unlikely(read_seqretry(>od->lock, seq)));
+ return ns;
+}
+
notrace static noinline void do_monotonic(struct timespec *ts)
{
- unsigned long seq, ns, secs;
+ unsigned long seq, ns;
do {
seq = read_seqbegin(>od->lock);
- 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_seqretry(>od->lock, seq)));
+ timespec_add_ns(ts, ns);
+}
- /* 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;
+notrace static noinline u64 do_monotonic_ns(void)
+{
+ unsigned long seq, ns;
+ do {
+ seq = read_seqbegin(>od->lock);
+ ns = gtod->monotonic_time_flat_ns + vgetns();
+ } while (unlikely(read_seqretry(>od->lock, seq)));
+ return ns;
}
notrace static noinline void do_realtime_coarse(struct timespec *ts)
@@ -126,26 +136,26 @@ notrace static noinline void do_realtime_coarse(struct timespec *ts)
} while (unlikely(read_seqretry(>od->lock, seq)));
}
+notrace static noinline u64 do_realtime_coarse_ns(void)
+{
+ /* This is atomic on x86-64. */
+ return ACCESS_ONCE(gtod->wall_time_coarse_flat_ns);
+}
+
notrace static noinline void do_monotonic_coarse(struct timespec *ts)
{
- unsigned long seq, ns, secs;
+ unsigned long seq;
do {
seq = read_seqbegin(>od->lock);
- 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_seqretry(>od->lock, 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;
+notrace static noinline u64 do_monotonic_coarse_ns(void)
+{
+ /* This is atomic on x86-64. */
+ return ACCESS_ONCE(gtod->monotonic_time_coarse_flat_ns);
}
notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
@@ -178,37 +188,38 @@ int clock_gettime(clockid_t, struct timespec *)
notrace int __vdso_clock_gettime_ns(clockid_t clock, struct timens *t)
{
- /* This implementation is slow. It will be improved later. */
-
struct timespec ts;
int error;
switch (clock) {
case CLOCK_REALTIME:
if (likely(gtod->clock.vclock_mode != VCLOCK_NONE)) {
- do_realtime(&ts);
- goto done;
+ t->ns = do_realtime_ns();
+ t->padding = 0;
+ return 0;
}
break;
case CLOCK_MONOTONIC:
if (likely(gtod->clock.vclock_mode != VCLOCK_NONE)) {
- do_monotonic(&ts);
- goto done;
+ t->ns = do_monotonic_ns();
+ t->padding = 0;
+ return 0;
}
break;
case CLOCK_REALTIME_COARSE:
- do_realtime_coarse(&ts);
- goto done;
+ t->ns = do_realtime_coarse_ns();
+ t->padding = 0;
+ return 0;
case CLOCK_MONOTONIC_COARSE:
- do_monotonic_coarse(&ts);
- goto done;
+ t->ns = do_monotonic_coarse_ns();
+ t->padding = 0;
+ return 0;
}
error = vdso_fallback_gettime(clock, &ts);
if (error)
return error;
-done:
t->ns = ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
t->padding = 0;
return 0;
--
1.7.7.4
--
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