Commit 951ed4d3 authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: default avatarjohn stultz <johnstul@us.ibm.com>
LKML-Reference: <20090707112728.3005244d@skybase>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent faf80d62

kernel/hrtimer.c

+4 −0
Original line number Diff line number Diff line
@@ -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 @@ 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
@@ -106,6 +108,7 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) = 
	}

};



#ifndef CONFIG_GENERIC_TIME

/**

 * ktime_get_ts - get the monotonic clock in timespec format

 * @ts:		pointer to timespec variable
@@ -130,6 +133,7 @@ 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

kernel/time/timekeeping.c

+69 −0
Original line number Diff line number Diff line
@@ -125,6 +125,75 @@ void getnstimeofday(struct timespec *ts) 


EXPORT_SYMBOL(getnstimeofday);



ktime_t ktime_get(void)

{

	cycle_t cycle_now, cycle_delta;

	unsigned int seq;

	s64 secs, nsecs;



	WARN_ON(timekeeping_suspended);



	do {

		seq = read_seqbegin(&xtime_lock);

		secs = xtime.tv_sec + wall_to_monotonic.tv_sec;

		nsecs = 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));

	/*

	 * Use ktime_set/ktime_add_ns to create a proper ktime on

	 * 32-bit architectures without CONFIG_KTIME_SCALAR.

	 */

	return ktime_add_ns(ktime_set(secs, 0), 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 int seq;

	s64 nsecs;



	WARN_ON(timekeeping_suspended);



	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

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