From: Richard Cochran Date: Wed, 31 Oct 2012 06:27:25 +0000 (+0000) Subject: time: remove the timecompare code. X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=65f8f9a1c1db831e5159e3e3e50912d1f214cd0c;p=deliverable%2Flinux.git 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 Acked-by: John Stultz Tested-by: Bob Liu Signed-off-by: David S. Miller --- diff --git a/include/linux/timecompare.h b/include/linux/timecompare.h deleted file mode 100644 index 546e2234e4b3..000000000000 --- a/include/linux/timecompare.h +++ /dev/null @@ -1,125 +0,0 @@ -/* - * Utility code which helps transforming between two different time - * bases, called "source" and "target" time in this code. - * - * Source time has to be provided via the timecounter API while target - * time is accessed via a function callback whose prototype - * intentionally matches ktime_get() and ktime_get_real(). These - * interfaces where chosen like this so that the code serves its - * initial purpose without additional glue code. - * - * This purpose is synchronizing a hardware clock in a NIC with system - * time, in order to implement the Precision Time Protocol (PTP, - * IEEE1588) with more accurate hardware assisted time stamping. In - * that context only synchronization against system time (= - * ktime_get_real()) is currently needed. But this utility code might - * become useful in other situations, which is why it was written as - * general purpose utility code. - * - * The source timecounter is assumed to return monotonically - * increasing time (but this code does its best to compensate if that - * is not the case) whereas target time may jump. - * - * The target time corresponding to a source time is determined by - * reading target time, reading source time, reading target time - * again, then assuming that average target time corresponds to source - * time. In other words, the assumption is that reading the source - * time is slow and involves equal time for sending the request and - * receiving the reply, whereas reading target time is assumed to be - * fast. - * - * Copyright (C) 2009 Intel Corporation. - * Author: Patrick Ohly - * - * This program is free software; you can redistribute it and/or modify it - * under the terms and conditions of the GNU General Public License, - * version 2, as published by the Free Software Foundation. - * - * This program is distributed in the hope 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., - * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA. - */ -#ifndef _LINUX_TIMECOMPARE_H -#define _LINUX_TIMECOMPARE_H - -#include -#include - -/** - * struct timecompare - stores state and configuration for the two clocks - * - * Initialize to zero, then set source/target/num_samples. - * - * Transformation between source time and target time is done with: - * target_time = source_time + offset + - * (source_time - last_update) * skew / - * TIMECOMPARE_SKEW_RESOLUTION - * - * @source: used to get source time stamps via timecounter_read() - * @target: function returning target time (for example, ktime_get - * for monotonic time, or ktime_get_real for wall clock) - * @num_samples: number of times that source time and target time are to - * be compared when determining their offset - * @offset: (target time - source time) at the time of the last update - * @skew: average (target time - source time) / delta source time * - * TIMECOMPARE_SKEW_RESOLUTION - * @last_update: last source time stamp when time offset was measured - */ -struct timecompare { - struct timecounter *source; - ktime_t (*target)(void); - int num_samples; - - s64 offset; - s64 skew; - u64 last_update; -}; - -/** - * timecompare_transform - transform source time stamp into target time base - * @sync: context for time sync - * @source_tstamp: the result of timecounter_read() or - * timecounter_cyc2time() - */ -extern ktime_t timecompare_transform(struct timecompare *sync, - u64 source_tstamp); - -/** - * timecompare_offset - measure current (target time - source time) offset - * @sync: context for time sync - * @offset: average offset during sample period returned here - * @source_tstamp: average source time during sample period returned here - * - * Returns number of samples used. Might be zero (= no result) in the - * unlikely case that target time was monotonically decreasing for all - * samples (= broken). - */ -extern int timecompare_offset(struct timecompare *sync, - s64 *offset, - u64 *source_tstamp); - -extern void __timecompare_update(struct timecompare *sync, - u64 source_tstamp); - -/** - * timecompare_update - update offset and skew by measuring current offset - * @sync: context for time sync - * @source_tstamp: the result of timecounter_read() or - * timecounter_cyc2time(), pass zero to force update - * - * Updates are only done at most once per second. - */ -static inline void timecompare_update(struct timecompare *sync, - u64 source_tstamp) -{ - if (!source_tstamp || - (s64)(source_tstamp - sync->last_update) >= NSEC_PER_SEC) - __timecompare_update(sync, source_tstamp); -} - -#endif /* _LINUX_TIMECOMPARE_H */ diff --git a/kernel/time/Makefile b/kernel/time/Makefile index e2fd74b8e8c2..ff7d9d2ab504 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 a9ae369925ce..000000000000 --- a/kernel/time/timecompare.c +++ /dev/null @@ -1,193 +0,0 @@ -/* - * Copyright (C) 2009 Intel Corporation. - * Author: Patrick Ohly - * - * 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 -#include -#include -#include -#include - -/* - * 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);