From 1aa5dfb751d275ae7117d3b73ac423b4a46f2a73 Mon Sep 17 00:00:00 2001
From: John Stultz <johnstul@us.ibm.com>
Date: Wed, 20 Aug 2008 16:37:28 -0700
Subject: clocksource: keep track of original clocksource frequency
The clocksource frequency is represented by
clocksource->mult/2^(clocksource->shift). Currently, when NTP makes
adjustments to the clock frequency, they are made directly to the mult
value.
This has the drawback that once changed, we cannot know what the orignal
mult value was, or how much adjustment has been applied.
This property causes problems in calculating proper ntp intervals when
switching back and forth between clocksources.
This patch separates the current mult value into a mult and mult_orig
pair. The mult_orig value stays constant, while the ntp clocksource
adjustments are done only to the mult value.
This allows for correct ntp interval calculation and additionally lays the
groundwork for a new notion of time, what I'm calling the monotonic-raw
time, which is introduced in a following patch.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/clocksource.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
(limited to 'include/linux/clocksource.h')
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 55e434feec9..f0a7fb98441 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -45,7 +45,8 @@ struct clocksource;
* @read: returns a cycle value
* @mask: bitmask for two's complement
* subtraction of non 64 bit counters
- * @mult: cycle to nanosecond multiplier
+ * @mult: cycle to nanosecond multiplier (adjusted by NTP)
+ * @mult_orig: cycle to nanosecond multiplier (unadjusted by NTP)
* @shift: cycle to nanosecond divisor (power of two)
* @flags: flags describing special properties
* @vread: vsyscall based read
@@ -63,6 +64,7 @@ struct clocksource {
cycle_t (*read)(void);
cycle_t mask;
u32 mult;
+ u32 mult_orig;
u32 shift;
unsigned long flags;
cycle_t (*vread)(void);
@@ -201,16 +203,17 @@ static inline void clocksource_calculate_interval(struct clocksource *c,
{
u64 tmp;
- /* XXX - All of this could use a whole lot of optimization */
+ /* Do the ns -> cycle conversion first, using original mult */
tmp = length_nsec;
tmp <<= c->shift;
- tmp += c->mult/2;
- do_div(tmp, c->mult);
+ tmp += c->mult_orig/2;
+ do_div(tmp, c->mult_orig);
c->cycle_interval = (cycle_t)tmp;
if (c->cycle_interval == 0)
c->cycle_interval = 1;
+ /* Go back from cycles -> shifted ns, this time use ntp adjused mult */
c->xtime_interval = (u64)c->cycle_interval * c->mult;
}
--
cgit v1.2.3-70-g09d2
From 2d42244ae71d6c7b0884b5664cf2eda30fb2ae68 Mon Sep 17 00:00:00 2001
From: John Stultz <johnstul@us.ibm.com>
Date: Wed, 20 Aug 2008 16:37:30 -0700
Subject: clocksource: introduce CLOCK_MONOTONIC_RAW
In talking with Josip Loncaric, and his work on clock synchronization (see
btime.sf.net), he mentioned that for really close synchronization, it is
useful to have access to "hardware time", that is a notion of time that is
not in any way adjusted by the clock slewing done to keep close time sync.
Part of the issue is if we are using the kernel's ntp adjusted
representation of time in order to measure how we should correct time, we
can run into what Paul McKenney aptly described as "Painting a road using
the lines we're painting as the guide".
I had been thinking of a similar problem, and was trying to come up with a
way to give users access to a purely hardware based time representation
that avoided users having to know the underlying frequency and mask values
needed to deal with the wide variety of possible underlying hardware
counters.
My solution is to introduce CLOCK_MONOTONIC_RAW. This exposes a
nanosecond based time value, that increments starting at bootup and has no
frequency adjustments made to it what so ever.
The time is accessed from userspace via the posix_clock_gettime() syscall,
passing CLOCK_MONOTONIC_RAW as the clock_id.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/clocksource.h | 3 +++
include/linux/time.h | 2 ++
kernel/posix-timers.c | 15 +++++++++++++++
kernel/time/timekeeping.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 64 insertions(+)
(limited to 'include/linux/clocksource.h')
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index f0a7fb98441..f88d32f8ff7 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -79,6 +79,7 @@ struct clocksource {
/* timekeeping specific data, ignore */
cycle_t cycle_interval;
u64 xtime_interval;
+ u32 raw_interval;
/*
* Second part is written at each timer interrupt
* Keep it in a different cache line to dirty no
@@ -87,6 +88,7 @@ struct clocksource {
cycle_t cycle_last ____cacheline_aligned_in_smp;
u64 xtime_nsec;
s64 error;
+ struct timespec raw_time;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
/* Watchdog related data, used by the framework */
@@ -215,6 +217,7 @@ static inline void clocksource_calculate_interval(struct clocksource *c,
/* Go back from cycles -> shifted ns, this time use ntp adjused mult */
c->xtime_interval = (u64)c->cycle_interval * c->mult;
+ c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) >> c->shift;
}
diff --git a/include/linux/time.h b/include/linux/time.h
index e15206a7e82..205f974b9eb 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -117,6 +117,7 @@ extern int do_setitimer(int which, struct itimerval *value,
extern unsigned int alarm_setitimer(unsigned int seconds);
extern int do_getitimer(int which, struct itimerval *value);
extern void getnstimeofday(struct timespec *tv);
+extern void getrawmonotonic(struct timespec *ts);
extern void getboottime(struct timespec *ts);
extern void monotonic_to_bootbased(struct timespec *ts);
@@ -214,6 +215,7 @@ struct itimerval {
#define CLOCK_MONOTONIC 1
#define CLOCK_PROCESS_CPUTIME_ID 2
#define CLOCK_THREAD_CPUTIME_ID 3
+#define CLOCK_MONOTONIC_RAW 4
/*
* The IDs of various hardware clocks:
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index e36d5798cbf..d3c66b53dff 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -222,6 +222,15 @@ static int posix_ktime_get_ts(clockid_t which_clock, struct timespec *tp)
return 0;
}
+/*
+ * Get monotonic time for posix timers
+ */
+static int posix_get_monotonic_raw(clockid_t which_clock, struct timespec *tp)
+{
+ getrawmonotonic(tp);
+ return 0;
+}
+
/*
* Initialize everything, well, just everything in Posix clocks/timers ;)
*/
@@ -235,9 +244,15 @@ static __init int init_posix_timers(void)
.clock_get = posix_ktime_get_ts,
.clock_set = do_posix_clock_nosettime,
};
+ struct k_clock clock_monotonic_raw = {
+ .clock_getres = hrtimer_get_res,
+ .clock_get = posix_get_monotonic_raw,
+ .clock_set = do_posix_clock_nosettime,
+ };
register_posix_clock(CLOCK_REALTIME, &clock_realtime);
register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic);
+ register_posix_clock(CLOCK_MONOTONIC_RAW, &clock_monotonic_raw);
posix_timers_cache = kmem_cache_create("posix_timers_cache",
sizeof (struct k_itimer), 0, SLAB_PANIC,
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 83d3555a699..5099c95b8aa 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -75,6 +75,9 @@ static void clocksource_forward_now(void)
nsec = cyc2ns(clock, cycle_delta);
timespec_add_ns(&xtime, nsec);
+
+ nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
+ clock->raw_time.tv_nsec += nsec;
}
/**
@@ -183,6 +186,8 @@ static void change_clocksource(void)
clocksource_forward_now();
+ new->raw_time = clock->raw_time;
+
clock = new;
clock->cycle_last = 0;
clock->cycle_last = clocksource_read(new);
@@ -204,6 +209,39 @@ static inline void clocksource_forward_now(void) { }
static inline void change_clocksource(void) { }
#endif
+/**
+ * getrawmonotonic - Returns the raw monotonic time in a timespec
+ * @ts: pointer to the timespec to be set
+ *
+ * Returns the raw monotonic time (completely un-modified by ntp)
+ */
+void getrawmonotonic(struct timespec *ts)
+{
+ unsigned long seq;
+ s64 nsecs;
+ cycle_t cycle_now, cycle_delta;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+
+ /* 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 = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
+
+ *ts = clock->raw_time;
+
+ } while (read_seqretry(&xtime_lock, seq));
+
+ timespec_add_ns(ts, nsecs);
+}
+EXPORT_SYMBOL(getrawmonotonic);
+
+
/**
* timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
*/
@@ -466,6 +504,12 @@ void update_wall_time(void)
second_overflow();
}
+ clock->raw_time.tv_nsec += clock->raw_interval;
+ if (clock->raw_time.tv_nsec >= NSEC_PER_SEC) {
+ clock->raw_time.tv_nsec -= NSEC_PER_SEC;
+ clock->raw_time.tv_sec++;
+ }
+
/* accumulate error between NTP and clock interval */
clock->error += tick_length;
clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
--
cgit v1.2.3-70-g09d2