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Date: Mon, 6 Jul 2009 15:49:33 +0200
From: Martin Schwidefsky <schwidefsky@...ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
john stultz <johnstul@...ibm.com>
Subject: [PATCH] optimized ktime_get[_ts] for GENERIC_TIME=y
From: Martin Schwidefsky <schwidefsky@...ibm.com>
The generic ktime_get function defined in kernel/hrtimer.c is suboptimial
for GENERIC_TIME=y:
0) | ktime_get() {
0) | ktime_get_ts() {
0) | getnstimeofday() {
0) | read_tod_clock() {
0) 0.601 us | }
0) 1.938 us | }
0) | set_normalized_timespec() {
0) 0.602 us | }
0) 4.375 us | }
0) 5.523 us | }
Overall there are two read_seqbegin/read_seqretry loops and a lot of
unnecessary struct timespec calculations. ktime_get returns a nano second
value which is the sum of xtime, wall_to_monotonic and the nano second
delta from the clock source.
ktime_get can be optimized for GENERIC_TIME=y. The new version only calls
clocksource_read:
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.610 us | }
0) 1.977 us | }
It uses a single read_seqbegin/readseqretry loop and just adds everthing
to a nano second value.
ktime_get_ts is optimized in a similar fashion.
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: john stultz <johnstul@...ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
---
kernel/hrtimer.c | 4 ++
kernel/time/timekeeping.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 67 insertions(+)
diff -urpN linux-2.5/kernel/hrtimer.c linux-2.5-patched/kernel/hrtimer.c
--- linux-2.5/kernel/hrtimer.c 2009-07-03 10:46:07.000000000 +0200
+++ linux-2.5-patched/kernel/hrtimer.c 2009-07-03 10:46:23.000000000 +0200
@@ -46,6 +46,7 @@
#include <asm/uaccess.h>
+#ifndef CONFIG_GENERIC_TIME
/**
* ktime_get - get the monotonic time in ktime_t format
*
@@ -60,6 +61,7 @@ ktime_t ktime_get(void)
return timespec_to_ktime(now);
}
EXPORT_SYMBOL_GPL(ktime_get);
+#endif
/**
* ktime_get_real - get the real (wall-) time in ktime_t format
@@ -104,6 +106,7 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base,
}
};
+#ifndef CONFIG_GENERIC_TIME
/**
* ktime_get_ts - get the monotonic clock in timespec format
* @ts: pointer to timespec variable
@@ -128,6 +131,7 @@ void ktime_get_ts(struct timespec *ts)
ts->tv_nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts);
+#endif
/*
* Get the coarse grained time at the softirq based on xtime and
diff -urpN linux-2.5/kernel/time/timekeeping.c linux-2.5-patched/kernel/time/timekeeping.c
--- linux-2.5/kernel/time/timekeeping.c 2009-07-03 10:46:07.000000000 +0200
+++ linux-2.5-patched/kernel/time/timekeeping.c 2009-07-03 10:46:23.000000000 +0200
@@ -118,6 +118,69 @@ void getnstimeofday(struct timespec *ts)
EXPORT_SYMBOL(getnstimeofday);
+ktime_t ktime_get(void)
+{
+ cycle_t cycle_now, cycle_delta;
+ struct timespec time;
+ unsigned long seq;
+ s64 nsecs;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ time.tv_sec = xtime.tv_sec + wall_to_monotonic.tv_sec;
+ time.tv_nsec = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
+
+ /* read clocksource: */
+ cycle_now = clocksource_read(clock);
+
+ /* calculate the delta since the last update_wall_time: */
+ cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+ /* convert to nanoseconds: */
+ nsecs = cyc2ns(clock, cycle_delta);
+
+ } while (read_seqretry(&xtime_lock, seq));
+ nsecs += time.tv_sec * 1000000000ULL + time.tv_nsec;
+ return (ktime_t) { .tv64 = nsecs };
+}
+EXPORT_SYMBOL_GPL(ktime_get);
+
+/**
+ * ktime_get_ts - get the monotonic clock in timespec format
+ * @ts: pointer to timespec variable
+ *
+ * The function calculates the monotonic clock from the realtime
+ * clock and the wall_to_monotonic offset and stores the result
+ * in normalized timespec format in the variable pointed to by @ts.
+ */
+void ktime_get_ts(struct timespec *ts)
+{
+ cycle_t cycle_now, cycle_delta;
+ struct timespec tomono;
+ unsigned long seq;
+ s64 nsecs;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ *ts = xtime;
+ tomono = wall_to_monotonic;
+
+ /* read clocksource: */
+ cycle_now = clocksource_read(clock);
+
+ /* calculate the delta since the last update_wall_time: */
+ cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+ /* convert to nanoseconds: */
+ nsecs = cyc2ns(clock, cycle_delta);
+
+ } while (read_seqretry(&xtime_lock, seq));
+
+ set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
+ ts->tv_nsec + tomono.tv_nsec + nsecs);
+}
+EXPORT_SYMBOL_GPL(ktime_get_ts);
+
/**
* do_gettimeofday - Returns the time of day in a timeval
* @tv: pointer to the timeval to be set
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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