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Subject[PATCH 5/7] time: Shadow cycle_last in timekeeper structure
Date
The clocksource cycle_last value is problematic for working on
shadow copies of the timekeeper, because the clocksource is global.

Since its mostly used only for timekeeping, move cycle_last into
the timekeeper. Unfortunately there are some uses for cycle_last
outside of timekeeping (such as tsc_read, which makes sure we haven't
skipped to a core that the TSC is behind the last read), so we
keep the clocksource cycle_last updated as well.

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 | 23 ++++++++++++++---------
1 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6c36d19..ebfb037 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -29,7 +29,8 @@ struct timekeeper {
u32 mult;
/* The shift value of the current clocksource. */
int shift;
-
+ /* cycle value at last accumulation point */
+ cycle_t cycle_last;
/* Number of clock cycles in one NTP interval. */
cycle_t cycle_interval;
/* Number of clock shifted nano seconds in one NTP interval. */
@@ -138,7 +139,8 @@ static void timekeeper_setup_internals(struct clocksource *clock)
u64 tmp, ntpinterval;

timekeeper.clock = clock;
- clock->cycle_last = clock->read(clock);
+ timekeeper.cycle_last = clock->read(clock);
+ clock->cycle_last = timekeeper.cycle_last;

/* Do the ns -> cycle conversion first, using original mult */
tmp = NTP_INTERVAL_LENGTH;
@@ -184,7 +186,7 @@ static inline s64 timekeeping_get_ns(void)
cycle_now = clock->read(clock);

/* calculate the delta since the last update_wall_time: */
- cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+ cycle_delta = (cycle_now - timekeeper.cycle_last) & clock->mask;

nsec = cycle_delta * timekeeper.mult + timekeeper.xtime_nsec;
return nsec >> timekeeper.shift;
@@ -200,7 +202,7 @@ static inline s64 timekeeping_get_ns_raw(void)
cycle_now = clock->read(clock);

/* calculate the delta since the last update_wall_time: */
- cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+ cycle_delta = (cycle_now - timekeeper.cycle_last) & clock->mask;

/* return delta convert to nanoseconds. */
return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
@@ -248,8 +250,9 @@ static void timekeeping_forward_now(void)

clock = timekeeper.clock;
cycle_now = clock->read(clock);
- cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
- clock->cycle_last = cycle_now;
+ cycle_delta = (cycle_now - timekeeper.cycle_last) & clock->mask;
+ timekeeper.cycle_last = cycle_now;
+ timekeeper.clock->cycle_last = cycle_now;

timekeeper.xtime_nsec += cycle_delta * timekeeper.mult;

@@ -749,7 +752,8 @@ static void timekeeping_resume(void)
__timekeeping_inject_sleeptime(&ts);
}
/* re-base the last cycle value */
- timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
+ timekeeper.cycle_last = timekeeper.clock->read(timekeeper.clock);
+ timekeeper.clock->cycle_last = timekeeper.cycle_last;
timekeeper.ntp_error = 0;
timekeeping_suspended = 0;

@@ -1016,7 +1020,7 @@ static cycle_t logarithmic_accumulation(struct timekeeper *tk, cycle_t offset,

/* Accumulate one shifted interval */
offset -= tk->cycle_interval << shift;
- tk->clock->cycle_last += tk->cycle_interval << shift;
+ tk->cycle_last += tk->cycle_interval << shift;

tk->xtime_nsec += tk->xtime_interval << shift;
while (tk->xtime_nsec >= nsecps) {
@@ -1070,7 +1074,7 @@ static void update_wall_time(void)
#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
offset = tk.cycle_interval;
#else
- offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
+ offset = (clock->read(clock) - tk.cycle_last) & clock->mask;
#endif

/*
@@ -1143,6 +1147,7 @@ static void update_wall_time(void)


timekeeper = tk;
+ timekeeper.clock->cycle_last = timekeeper.cycle_last;
timekeeping_update(&timekeeper, false);

out:
--
1.7.3.2.146.gca209


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