[deliverable/linux.git] / kernel / time / timecompare.c

/*
 * Copyright (C) 2009 Intel Corporation.
 * Author: Patrick Ohly <patrick.ohly@intel.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/timecompare.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/math64.h>
#include <linux/kernel.h>

/*
 * fixed point arithmetic scale factor for skew
 *
 * Usually one would measure skew in ppb (parts per billion, 1e9), but
 * using a factor of 2 simplifies the math.
 */
#define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30)

ktime_t timecompare_transform(struct timecompare *sync,
			      u64 source_tstamp)
{
	u64 nsec;

	nsec = source_tstamp + sync->offset;
	nsec += (s64)(source_tstamp - sync->last_update) * sync->skew /
		TIMECOMPARE_SKEW_RESOLUTION;

	return ns_to_ktime(nsec);
}
EXPORT_SYMBOL_GPL(timecompare_transform);

int timecompare_offset(struct timecompare *sync,
		       s64 *offset,
		       u64 *source_tstamp)
{
	u64 start_source = 0, end_source = 0;
	struct {
		s64 offset;
		s64 duration_target;
	} buffer[10], sample, *samples;
	int counter = 0, i;
	int used;
	int index;
	int num_samples = sync->num_samples;

	if (num_samples > ARRAY_SIZE(buffer)) {
		samples = kmalloc(sizeof(*samples) * num_samples, GFP_ATOMIC);
		if (!samples) {
			samples = buffer;
			num_samples = ARRAY_SIZE(buffer);
		}
	} else {
		samples = buffer;
	}

	/* run until we have enough valid samples, but do not try forever */
	i = 0;
	counter = 0;
	while (1) {
		u64 ts;
		ktime_t start, end;

		start = sync->target();
		ts = timecounter_read(sync->source);
		end = sync->target();

		if (!i)
			start_source = ts;

		/* ignore negative durations */
		sample.duration_target = ktime_to_ns(ktime_sub(end, start));
		if (sample.duration_target >= 0) {
			/*
			 * assume symetric delay to and from source:
			 * average target time corresponds to measured
			 * source time
			 */
			sample.offset =
				(ktime_to_ns(end) + ktime_to_ns(start)) / 2 -
				ts;

			/* simple insertion sort based on duration */
			index = counter - 1;
			while (index >= 0) {
				if (samples[index].duration_target <
				    sample.duration_target)
					break;
				samples[index + 1] = samples[index];
				index--;
			}
			samples[index + 1] = sample;
			counter++;
		}

		i++;
		if (counter >= num_samples || i >= 100000) {
			end_source = ts;
			break;
		}
	}

	*source_tstamp = (end_source + start_source) / 2;

	/* remove outliers by only using 75% of the samples */
	used = counter * 3 / 4;
	if (!used)
		used = counter;
	if (used) {
		/* calculate average */
		s64 off = 0;
		for (index = 0; index < used; index++)
			off += samples[index].offset;
		*offset = div_s64(off, used);
	}

	if (samples && samples != buffer)
		kfree(samples);

	return used;
}
EXPORT_SYMBOL_GPL(timecompare_offset);

void __timecompare_update(struct timecompare *sync,
			  u64 source_tstamp)
{
	s64 offset;
	u64 average_time;

	if (!timecompare_offset(sync, &offset, &average_time))
		return;

	if (!sync->last_update) {
		sync->last_update = average_time;
		sync->offset = offset;
		sync->skew = 0;
	} else {
		s64 delta_nsec = average_time - sync->last_update;

		/* avoid division by negative or small deltas */
		if (delta_nsec >= 10000) {
			s64 delta_offset_nsec = offset - sync->offset;
			s64 skew; /* delta_offset_nsec *
				     TIMECOMPARE_SKEW_RESOLUTION /
				     delta_nsec */
			u64 divisor;

			/* div_s64() is limited to 32 bit divisor */
			skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION;
			divisor = delta_nsec;
			while (unlikely(divisor >= ((s64)1) << 32)) {
				/* divide both by 2; beware, right shift
				   of negative value has undefined
				   behavior and can only be used for
				   the positive divisor */
				skew = div_s64(skew, 2);
				divisor >>= 1;
			}
			skew = div_s64(skew, divisor);

			/*
			 * Calculate new overall skew as 4/16 the
			 * old value and 12/16 the new one. This is
			 * a rather arbitrary tradeoff between
			 * only using the latest measurement (0/16 and
			 * 16/16) and even more weight on past measurements.
			 */
#define TIMECOMPARE_NEW_SKEW_PER_16 12
			sync->skew =
				div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) *
					sync->skew +
					TIMECOMPARE_NEW_SKEW_PER_16 * skew,
					16);
			sync->last_update = average_time;
			sync->offset = offset;
		}
	}
}
EXPORT_SYMBOL_GPL(__timecompare_update);
Commit	Line	Data
a75244c3 PO	1	/*
	2	* Copyright (C) 2009 Intel Corporation.
	3	* Author: Patrick Ohly <patrick.ohly@intel.com>
	4	*
	5	* This program is free software; you can redistribute it and/or modify
	6	* it under the terms of the GNU General Public License as published by
	7	* the Free Software Foundation; either version 2 of the License, or
	8	* (at your option) any later version.
	9	*
	10	* This program is distributed in the hope that it will be useful,
	11	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	13	* GNU General Public License for more details.
	14	*
	15	* You should have received a copy of the GNU General Public License
	16	* along with this program; if not, write to the Free Software
	17	* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
	18	*/
	19
	20	#include <linux/timecompare.h>
	21	#include <linux/module.h>
5a0e3ad6	22	#include <linux/slab.h>
a75244c3	23	#include <linux/math64.h>
2bf1c05e	24	#include <linux/kernel.h>
a75244c3 PO	25
	26	/*
	27	* fixed point arithmetic scale factor for skew
	28	*
	29	* Usually one would measure skew in ppb (parts per billion, 1e9), but
	30	* using a factor of 2 simplifies the math.
	31	*/
	32	#define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30)
	33
	34	ktime_t timecompare_transform(struct timecompare *sync,
	35	u64 source_tstamp)
	36	{
	37	u64 nsec;
	38
	39	nsec = source_tstamp + sync->offset;
	40	nsec += (s64)(source_tstamp - sync->last_update) * sync->skew /
	41	TIMECOMPARE_SKEW_RESOLUTION;
	42
	43	return ns_to_ktime(nsec);
	44	}
3586e0a9	45	EXPORT_SYMBOL_GPL(timecompare_transform);
a75244c3 PO	46
	47	int timecompare_offset(struct timecompare *sync,
	48	s64 *offset,
	49	u64 *source_tstamp)
	50	{
	51	u64 start_source = 0, end_source = 0;
	52	struct {
	53	s64 offset;
	54	s64 duration_target;
	55	} buffer[10], sample, *samples;
	56	int counter = 0, i;
	57	int used;
	58	int index;
	59	int num_samples = sync->num_samples;
	60
2bf1c05e	61	if (num_samples > ARRAY_SIZE(buffer)) {
a75244c3 PO	62	samples = kmalloc(sizeof(samples) num_samples, GFP_ATOMIC);
	63	if (!samples) {
	64	samples = buffer;
2bf1c05e	65	num_samples = ARRAY_SIZE(buffer);
a75244c3 PO	66	}
	67	} else {
	68	samples = buffer;
	69	}
	70
	71	/* run until we have enough valid samples, but do not try forever */
	72	i = 0;
	73	counter = 0;
	74	while (1) {
	75	u64 ts;
	76	ktime_t start, end;
	77
	78	start = sync->target();
	79	ts = timecounter_read(sync->source);
	80	end = sync->target();
	81
	82	if (!i)
	83	start_source = ts;
	84
	85	/* ignore negative durations */
	86	sample.duration_target = ktime_to_ns(ktime_sub(end, start));
	87	if (sample.duration_target >= 0) {
	88	/*
	89	* assume symetric delay to and from source:
	90	* average target time corresponds to measured
	91	* source time
	92	*/
	93	sample.offset =
f065f41f	94	(ktime_to_ns(end) + ktime_to_ns(start)) / 2 -
a75244c3 PO	95	ts;
	96
	97	/* simple insertion sort based on duration */
	98	index = counter - 1;
	99	while (index >= 0) {
	100	if (samples[index].duration_target <
	101	sample.duration_target)
	102	break;
	103	samples[index + 1] = samples[index];
	104	index--;
	105	}
	106	samples[index + 1] = sample;
	107	counter++;
	108	}
	109
	110	i++;
	111	if (counter >= num_samples \|\| i >= 100000) {
	112	end_source = ts;
	113	break;
	114	}
	115	}
	116
	117	*source_tstamp = (end_source + start_source) / 2;
	118
	119	/* remove outliers by only using 75% of the samples */
	120	used = counter * 3 / 4;
	121	if (!used)
	122	used = counter;
	123	if (used) {
	124	/* calculate average */
	125	s64 off = 0;
	126	for (index = 0; index < used; index++)
	127	off += samples[index].offset;
	128	*offset = div_s64(off, used);
	129	}
	130
	131	if (samples && samples != buffer)
	132	kfree(samples);
	133
	134	return used;
	135	}
3586e0a9	136	EXPORT_SYMBOL_GPL(timecompare_offset);
a75244c3 PO	137
	138	void __timecompare_update(struct timecompare *sync,
	139	u64 source_tstamp)
	140	{
	141	s64 offset;
	142	u64 average_time;
	143
	144	if (!timecompare_offset(sync, &offset, &average_time))
	145	return;
	146
	147	if (!sync->last_update) {
	148	sync->last_update = average_time;
	149	sync->offset = offset;
	150	sync->skew = 0;
	151	} else {
	152	s64 delta_nsec = average_time - sync->last_update;
	153
	154	/* avoid division by negative or small deltas */
	155	if (delta_nsec >= 10000) {
	156	s64 delta_offset_nsec = offset - sync->offset;
	157	s64 skew; /* delta_offset_nsec *
	158	TIMECOMPARE_SKEW_RESOLUTION /
	159	delta_nsec */
	160	u64 divisor;
	161
	162	/* div_s64() is limited to 32 bit divisor */
	163	skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION;
	164	divisor = delta_nsec;
	165	while (unlikely(divisor >= ((s64)1) << 32)) {
	166	/* divide both by 2; beware, right shift
	167	of negative value has undefined
	168	behavior and can only be used for
	169	the positive divisor */
	170	skew = div_s64(skew, 2);
	171	divisor >>= 1;
	172	}
	173	skew = div_s64(skew, divisor);
	174
	175	/*
	176	* Calculate new overall skew as 4/16 the
	177	* old value and 12/16 the new one. This is
	178	* a rather arbitrary tradeoff between
	179	* only using the latest measurement (0/16 and
	180	* 16/16) and even more weight on past measurements.
	181	*/
	182	#define TIMECOMPARE_NEW_SKEW_PER_16 12
	183	sync->skew =
	184	div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) *
	185	sync->skew +
	186	TIMECOMPARE_NEW_SKEW_PER_16 * skew,
	187	16);
	188	sync->last_update = average_time;
	189	sync->offset = offset;
	190	}
	191	}
	192	}
3586e0a9	193	EXPORT_SYMBOL_GPL(__timecompare_update);