timekeeping: optimized ktime_get[_ts] for GENERIC_TIME=y
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.
[ tglx: added WARN_ON(timekeeping_suspended) as in getnstimeofday() ]
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: john stultz <johnstul@us.ibm.com>
LKML-Reference: <20090707112728.3005244d@skybase>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 9002958..829e066 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -48,6 +48,7 @@
#include <asm/uaccess.h>
+#ifndef CONFIG_GENERIC_TIME
/**
* ktime_get - get the monotonic time in ktime_t format
*
@@ -62,6 +63,7 @@
return timespec_to_ktime(now);
}
EXPORT_SYMBOL_GPL(ktime_get);
+#endif
/**
* ktime_get_real - get the real (wall-) time in ktime_t format
@@ -106,6 +108,7 @@
}
};
+#ifndef CONFIG_GENERIC_TIME
/**
* ktime_get_ts - get the monotonic clock in timespec format
* @ts: pointer to timespec variable
@@ -130,6 +133,7 @@
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