time: remove the timecompare code.
This patch removes the timecompare code from the kernel. The top five
reasons to do this are:
1. There are no more users of this code.
2. The original idea was a bit weak.
3. The original author has disappeared.
4. The code was not general purpose but tuned to a particular hardware,
5. There are better ways to accomplish clock synchronization.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Tested-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index e2fd74b..ff7d9d2 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -1,4 +1,4 @@
-obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o timecompare.o
+obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o
obj-y += timeconv.o posix-clock.o alarmtimer.o
obj-$(CONFIG_GENERIC_CLOCKEVENTS_BUILD) += clockevents.o
diff --git a/kernel/time/timecompare.c b/kernel/time/timecompare.c
deleted file mode 100644
index a9ae369..0000000
--- a/kernel/time/timecompare.c
+++ /dev/null
@@ -1,193 +0,0 @@
-/*
- * 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);