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Subject[PATCH 4/9] time: Update timekeeper structure using a local shadow
Date
Uses a local shadow structure to update the timekeeper. This
will allow for reduced timekeeper.rlock hold time.

CC: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
kernel/time/timekeeping.c | 43 +++++++++++++++++++++++--------------------
1 files changed, 23 insertions(+), 20 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index f9ee96c..09460c1 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -74,6 +74,7 @@ struct timekeeper {
};

static struct timekeeper timekeeper;
+static struct timekeeper shadow_tk;

/* Locks for timekeeper variable: */
/* This seqcount serializes readers from updates */
@@ -1072,10 +1073,11 @@ static void update_wall_time(void)
if (unlikely(timekeeping_suspended))
goto out;

- clock = timekeeper.clock;
+ shadow_tk = timekeeper;
+ clock = shadow_tk.clock;

#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
- offset = timekeeper.cycle_interval;
+ offset = shadow_tk.cycle_interval;
#else
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif
@@ -1088,19 +1090,19 @@ static void update_wall_time(void)
* chunk in one go, and then try to consume the next smaller
* doubled multiple.
*/
- shift = ilog2(offset) - ilog2(timekeeper.cycle_interval);
+ shift = ilog2(offset) - ilog2(shadow_tk.cycle_interval);
shift = max(0, shift);
/* Bound shift to one less then what overflows tick_length */
maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1;
shift = min(shift, maxshift);
- while (offset >= timekeeper.cycle_interval) {
- offset = logarithmic_accumulation(&timekeeper, offset, shift);
- if(offset < timekeeper.cycle_interval<<shift)
+ while (offset >= shadow_tk.cycle_interval) {
+ offset = logarithmic_accumulation(&shadow_tk, offset, shift);
+ if (offset < shadow_tk.cycle_interval<<shift)
shift--;
}

/* correct the clock when NTP error is too big */
- timekeeping_adjust(&timekeeper, offset);
+ timekeeping_adjust(&shadow_tk, offset);

/*
* Since in the loop above, we accumulate any amount of time
@@ -1118,10 +1120,10 @@ static void update_wall_time(void)
* We'll correct this error next time through this function, when
* xtime_nsec is not as small.
*/
- if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
- s64 neg = -(s64)timekeeper.xtime_nsec;
- timekeeper.xtime_nsec = 0;
- timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
+ if (unlikely((s64)shadow_tk.xtime_nsec < 0)) {
+ s64 neg = -(s64)shadow_tk.xtime_nsec;
+ shadow_tk.xtime_nsec = 0;
+ shadow_tk.ntp_error += neg << shadow_tk.ntp_error_shift;
}

/*
@@ -1133,23 +1135,24 @@ static void update_wall_time(void)
* the vsyscall implementations are converted to use xtime_nsec
* (shifted nanoseconds), this can be killed.
*/
- remainder = timekeeper.xtime_nsec & ((1<<timekeeper.shift)-1);
- timekeeper.xtime_nsec -= remainder;
- timekeeper.xtime_nsec += 1<<timekeeper.shift;
- timekeeper.ntp_error += remainder <<
- timekeeper.ntp_error_shift;
+ remainder = shadow_tk.xtime_nsec & ((1<<shadow_tk.shift)-1);
+ shadow_tk.xtime_nsec -= remainder;
+ shadow_tk.xtime_nsec += 1<<shadow_tk.shift;
+ shadow_tk.ntp_error += remainder << shadow_tk.ntp_error_shift;

/*
* Finally, make sure that after the rounding
* xtime.tv_nsec isn't larger then NSEC_PER_SEC
*/
- if (unlikely(timekeeper.xtime_nsec >=
- ((u64)NSEC_PER_SEC << timekeeper.shift))) {
- timekeeper.xtime_nsec -= (u64)NSEC_PER_SEC << timekeeper.shift;
- timekeeper.xtime_sec++;
+ if (unlikely(shadow_tk.xtime_nsec >=
+ ((u64)NSEC_PER_SEC << shadow_tk.shift))) {
+ shadow_tk.xtime_nsec -= (u64)NSEC_PER_SEC << shadow_tk.shift;
+ shadow_tk.xtime_sec++;
second_overflow();
}

+
+ timekeeper = shadow_tk;
timekeeping_update(&timekeeper, false);

out:
--
1.7.3.2.146.gca209


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