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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>
This commit is contained in:
Richard Cochran
David S. Miller
parent
dd87b22f90
commit
65f8f9a1c1
@ -1,125 +0,0 @@
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/*
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* Utility code which helps transforming between two different time
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* bases, called "source" and "target" time in this code.
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*
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* Source time has to be provided via the timecounter API while target
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* time is accessed via a function callback whose prototype
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* intentionally matches ktime_get() and ktime_get_real(). These
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* interfaces where chosen like this so that the code serves its
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* initial purpose without additional glue code.
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*
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* This purpose is synchronizing a hardware clock in a NIC with system
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* time, in order to implement the Precision Time Protocol (PTP,
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* IEEE1588) with more accurate hardware assisted time stamping. In
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* that context only synchronization against system time (=
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* ktime_get_real()) is currently needed. But this utility code might
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* become useful in other situations, which is why it was written as
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* general purpose utility code.
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*
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* The source timecounter is assumed to return monotonically
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* increasing time (but this code does its best to compensate if that
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* is not the case) whereas target time may jump.
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*
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* The target time corresponding to a source time is determined by
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* reading target time, reading source time, reading target time
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* again, then assuming that average target time corresponds to source
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* time. In other words, the assumption is that reading the source
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* time is slow and involves equal time for sending the request and
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* receiving the reply, whereas reading target time is assumed to be
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* fast.
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*
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* Copyright (C) 2009 Intel Corporation.
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* Author: Patrick Ohly <patrick.ohly@intel.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. * See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#ifndef _LINUX_TIMECOMPARE_H
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#define _LINUX_TIMECOMPARE_H
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#include <linux/clocksource.h>
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#include <linux/ktime.h>
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/**
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* struct timecompare - stores state and configuration for the two clocks
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*
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* Initialize to zero, then set source/target/num_samples.
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*
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* Transformation between source time and target time is done with:
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* target_time = source_time + offset +
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* (source_time - last_update) * skew /
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* TIMECOMPARE_SKEW_RESOLUTION
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*
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* @source: used to get source time stamps via timecounter_read()
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* @target: function returning target time (for example, ktime_get
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* for monotonic time, or ktime_get_real for wall clock)
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* @num_samples: number of times that source time and target time are to
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* be compared when determining their offset
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* @offset: (target time - source time) at the time of the last update
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* @skew: average (target time - source time) / delta source time *
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* TIMECOMPARE_SKEW_RESOLUTION
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* @last_update: last source time stamp when time offset was measured
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*/
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struct timecompare {
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struct timecounter *source;
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ktime_t (*target)(void);
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int num_samples;
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s64 offset;
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s64 skew;
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u64 last_update;
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};
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/**
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* timecompare_transform - transform source time stamp into target time base
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* @sync: context for time sync
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* @source_tstamp: the result of timecounter_read() or
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* timecounter_cyc2time()
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*/
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extern ktime_t timecompare_transform(struct timecompare *sync,
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u64 source_tstamp);
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/**
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* timecompare_offset - measure current (target time - source time) offset
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* @sync: context for time sync
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* @offset: average offset during sample period returned here
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* @source_tstamp: average source time during sample period returned here
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*
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* Returns number of samples used. Might be zero (= no result) in the
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* unlikely case that target time was monotonically decreasing for all
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* samples (= broken).
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*/
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extern int timecompare_offset(struct timecompare *sync,
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s64 *offset,
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u64 *source_tstamp);
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extern void __timecompare_update(struct timecompare *sync,
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u64 source_tstamp);
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/**
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* timecompare_update - update offset and skew by measuring current offset
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* @sync: context for time sync
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* @source_tstamp: the result of timecounter_read() or
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* timecounter_cyc2time(), pass zero to force update
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*
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* Updates are only done at most once per second.
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*/
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static inline void timecompare_update(struct timecompare *sync,
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u64 source_tstamp)
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{
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if (!source_tstamp ||
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(s64)(source_tstamp - sync->last_update) >= NSEC_PER_SEC)
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__timecompare_update(sync, source_tstamp);
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}
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#endif /* _LINUX_TIMECOMPARE_H */
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@ -1,4 +1,4 @@
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obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o timecompare.o
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obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o
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obj-y += timeconv.o posix-clock.o alarmtimer.o
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obj-$(CONFIG_GENERIC_CLOCKEVENTS_BUILD) += clockevents.o
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@ -1,193 +0,0 @@
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/*
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* Copyright (C) 2009 Intel Corporation.
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* Author: Patrick Ohly <patrick.ohly@intel.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <linux/timecompare.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/math64.h>
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#include <linux/kernel.h>
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/*
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* fixed point arithmetic scale factor for skew
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*
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* Usually one would measure skew in ppb (parts per billion, 1e9), but
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* using a factor of 2 simplifies the math.
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*/
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#define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30)
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ktime_t timecompare_transform(struct timecompare *sync,
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u64 source_tstamp)
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{
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u64 nsec;
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nsec = source_tstamp + sync->offset;
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nsec += (s64)(source_tstamp - sync->last_update) * sync->skew /
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TIMECOMPARE_SKEW_RESOLUTION;
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return ns_to_ktime(nsec);
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}
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EXPORT_SYMBOL_GPL(timecompare_transform);
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int timecompare_offset(struct timecompare *sync,
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s64 *offset,
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u64 *source_tstamp)
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{
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u64 start_source = 0, end_source = 0;
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struct {
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s64 offset;
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s64 duration_target;
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} buffer[10], sample, *samples;
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int counter = 0, i;
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int used;
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int index;
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int num_samples = sync->num_samples;
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if (num_samples > ARRAY_SIZE(buffer)) {
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samples = kmalloc(sizeof(*samples) * num_samples, GFP_ATOMIC);
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if (!samples) {
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samples = buffer;
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num_samples = ARRAY_SIZE(buffer);
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}
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} else {
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samples = buffer;
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}
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/* run until we have enough valid samples, but do not try forever */
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i = 0;
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counter = 0;
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while (1) {
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u64 ts;
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ktime_t start, end;
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start = sync->target();
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ts = timecounter_read(sync->source);
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end = sync->target();
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if (!i)
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start_source = ts;
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/* ignore negative durations */
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sample.duration_target = ktime_to_ns(ktime_sub(end, start));
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if (sample.duration_target >= 0) {
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/*
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* assume symetric delay to and from source:
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* average target time corresponds to measured
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* source time
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*/
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sample.offset =
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(ktime_to_ns(end) + ktime_to_ns(start)) / 2 -
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ts;
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/* simple insertion sort based on duration */
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index = counter - 1;
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while (index >= 0) {
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if (samples[index].duration_target <
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sample.duration_target)
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break;
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samples[index + 1] = samples[index];
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index--;
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}
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samples[index + 1] = sample;
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counter++;
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}
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i++;
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if (counter >= num_samples || i >= 100000) {
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end_source = ts;
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break;
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}
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}
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*source_tstamp = (end_source + start_source) / 2;
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/* remove outliers by only using 75% of the samples */
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used = counter * 3 / 4;
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if (!used)
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used = counter;
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if (used) {
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/* calculate average */
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s64 off = 0;
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for (index = 0; index < used; index++)
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off += samples[index].offset;
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*offset = div_s64(off, used);
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}
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if (samples && samples != buffer)
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kfree(samples);
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return used;
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}
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EXPORT_SYMBOL_GPL(timecompare_offset);
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void __timecompare_update(struct timecompare *sync,
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u64 source_tstamp)
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{
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s64 offset;
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u64 average_time;
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if (!timecompare_offset(sync, &offset, &average_time))
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return;
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if (!sync->last_update) {
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sync->last_update = average_time;
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sync->offset = offset;
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sync->skew = 0;
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} else {
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s64 delta_nsec = average_time - sync->last_update;
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/* avoid division by negative or small deltas */
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if (delta_nsec >= 10000) {
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s64 delta_offset_nsec = offset - sync->offset;
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s64 skew; /* delta_offset_nsec *
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TIMECOMPARE_SKEW_RESOLUTION /
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delta_nsec */
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u64 divisor;
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/* div_s64() is limited to 32 bit divisor */
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skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION;
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divisor = delta_nsec;
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while (unlikely(divisor >= ((s64)1) << 32)) {
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/* divide both by 2; beware, right shift
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of negative value has undefined
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behavior and can only be used for
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the positive divisor */
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skew = div_s64(skew, 2);
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divisor >>= 1;
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}
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skew = div_s64(skew, divisor);
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/*
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* Calculate new overall skew as 4/16 the
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* old value and 12/16 the new one. This is
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* a rather arbitrary tradeoff between
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* only using the latest measurement (0/16 and
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* 16/16) and even more weight on past measurements.
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*/
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#define TIMECOMPARE_NEW_SKEW_PER_16 12
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sync->skew =
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div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) *
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sync->skew +
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TIMECOMPARE_NEW_SKEW_PER_16 * skew,
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16);
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sync->last_update = average_time;
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sync->offset = offset;
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}
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}
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}
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EXPORT_SYMBOL_GPL(__timecompare_update);
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