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Date: Tue, 6 Apr 2010 14:30:51 -0700
From: John Stultz <johnstul@...ibm.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: John Stultz <johnstul@...ibm.com>,
Petr Titěra <P.Titera@...tury.cz>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] time: remove xtime_cache (take 2)
Thomas: Mind queueing this up for 2.6.35?
With the earlier logarithmic time accumulation patch, xtime will now
always be within one "tick" of the current time, instead of possibly
half a second off.
This removes the need for the xtime_cache value, which always stored the
time at the last interrupt, so this patch cleans that up removing the
xtime_cache related code.
This patch also addresses an issue with an earlier version of this change,
where xtime_cache was normalizing xtime, which could in some cases be
not valid (ie: tv_nsec == NSEC_PER_SEC). This is fixed by handling
the edge case in update_wall_time().
Cc: Petr Titěra <P.Titera@...tury.cz>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: John Stultz <johnstul@...ibm.com>
---
include/linux/time.h | 1 -
kernel/time.c | 1 -
kernel/time/timekeeping.c | 35 ++++++++++++++++-------------------
3 files changed, 16 insertions(+), 21 deletions(-)
diff --git a/include/linux/time.h b/include/linux/time.h
index 6e026e4..ea3559f 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -150,7 +150,6 @@ extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
extern int timekeeping_valid_for_hres(void);
extern u64 timekeeping_max_deferment(void);
extern void update_wall_time(void);
-extern void update_xtime_cache(u64 nsec);
extern void timekeeping_leap_insert(int leapsecond);
struct tms;
diff --git a/kernel/time.c b/kernel/time.c
index 656dccf..129fe12 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -135,7 +135,6 @@ static inline void warp_clock(void)
write_seqlock_irq(&xtime_lock);
wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
xtime.tv_sec += sys_tz.tz_minuteswest * 60;
- update_xtime_cache(0);
write_sequnlock_irq(&xtime_lock);
clock_was_set();
}
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 39f6177..dec9175 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -165,13 +165,6 @@ struct timespec raw_time;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
-static struct timespec xtime_cache __attribute__ ((aligned (16)));
-void update_xtime_cache(u64 nsec)
-{
- xtime_cache = xtime;
- timespec_add_ns(&xtime_cache, nsec);
-}
-
/* must hold xtime_lock */
void timekeeping_leap_insert(int leapsecond)
{
@@ -332,8 +325,6 @@ int do_settimeofday(struct timespec *tv)
xtime = *tv;
- update_xtime_cache(0);
-
timekeeper.ntp_error = 0;
ntp_clear();
@@ -559,7 +550,6 @@ void __init timekeeping_init(void)
}
set_normalized_timespec(&wall_to_monotonic,
-boot.tv_sec, -boot.tv_nsec);
- update_xtime_cache(0);
total_sleep_time.tv_sec = 0;
total_sleep_time.tv_nsec = 0;
write_sequnlock_irqrestore(&xtime_lock, flags);
@@ -593,7 +583,6 @@ static int timekeeping_resume(struct sys_device *dev)
wall_to_monotonic = timespec_sub(wall_to_monotonic, ts);
total_sleep_time = timespec_add_safe(total_sleep_time, ts);
}
- update_xtime_cache(0);
/* re-base the last cycle value */
timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
timekeeper.ntp_error = 0;
@@ -788,7 +777,6 @@ void update_wall_time(void)
{
struct clocksource *clock;
cycle_t offset;
- u64 nsecs;
int shift = 0, maxshift;
/* Make sure we're fully resumed: */
@@ -847,7 +835,9 @@ void update_wall_time(void)
timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
}
- /* store full nanoseconds into xtime after rounding it up and
+
+ /*
+ * Store full nanoseconds into xtime after rounding it up and
* add the remainder to the error difference.
*/
xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
@@ -855,8 +845,15 @@ void update_wall_time(void)
timekeeper.ntp_error += timekeeper.xtime_nsec <<
timekeeper.ntp_error_shift;
- nsecs = clocksource_cyc2ns(offset, timekeeper.mult, timekeeper.shift);
- update_xtime_cache(nsecs);
+ /*
+ * Finally, make sure that after the rounding
+ * xtime.tv_nsec isn't larger then NSEC_PER_SEC
+ */
+ if (unlikely(xtime.tv_nsec >= NSEC_PER_SEC)) {
+ xtime.tv_nsec -= NSEC_PER_SEC;
+ xtime.tv_sec++;
+ second_overflow();
+ }
/* check to see if there is a new clocksource to use */
update_vsyscall(&xtime, timekeeper.clock, timekeeper.mult);
@@ -896,13 +893,13 @@ EXPORT_SYMBOL_GPL(monotonic_to_bootbased);
unsigned long get_seconds(void)
{
- return xtime_cache.tv_sec;
+ return xtime.tv_sec;
}
EXPORT_SYMBOL(get_seconds);
struct timespec __current_kernel_time(void)
{
- return xtime_cache;
+ return xtime;
}
struct timespec current_kernel_time(void)
@@ -913,7 +910,7 @@ struct timespec current_kernel_time(void)
do {
seq = read_seqbegin(&xtime_lock);
- now = xtime_cache;
+ now = xtime;
} while (read_seqretry(&xtime_lock, seq));
return now;
@@ -928,7 +925,7 @@ struct timespec get_monotonic_coarse(void)
do {
seq = read_seqbegin(&xtime_lock);
- now = xtime_cache;
+ now = xtime;
mono = wall_to_monotonic;
} while (read_seqretry(&xtime_lock, seq));
--
1.6.0.4
--
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