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Subject[PATCH 3/7] time: Split timekeeper lock into separate reader/writer locks
Date
In order to reduce the lock hold time, split the timekeeper lock
into a writer lock, which serializes updates to the timekeeper
structure, and a reader sequence counter, which ensures readers
see a consistent version of the timekeeper.

This will allow us to reduce the lock wait time for readers, by
doing updates on a shadow copy of the timekeeper.

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 | 113 +++++++++++++++++++++++++++------------------
1 files changed, 68 insertions(+), 45 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 9e6b28e..4962284 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -71,8 +71,9 @@ struct timekeeper {
/* The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock. */
struct timespec raw_time;

- /* Seqlock for all timekeeper values */
- seqlock_t lock;
+ /* locks for timekeeper structure */
+ seqcount_t rlock; /* This seqcount serializes readers from updates */
+ spinlock_t wlock; /* This spinlock serializes updaters */
};

static struct timekeeper timekeeper;
@@ -205,7 +206,7 @@ static inline s64 timekeeping_get_ns_raw(void)
return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
}

-/* must hold write on timekeeper.lock */
+/* must hold write on timekeeper.wlock */
static void timekeeping_update(struct timekeeper *tk, bool clearntp)
{
struct timespec xt;
@@ -222,11 +223,13 @@ void timekeeping_leap_insert(int leapsecond)
{
unsigned long flags;

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);
timekeeper.xtime_sec += leapsecond;
timekeeper.wall_to_monotonic.tv_sec -= leapsecond;
timekeeping_update(&timekeeper, false);
- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

}

@@ -273,7 +276,7 @@ void getnstimeofday(struct timespec *ts)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

ts->tv_sec = timekeeper.xtime_sec;
ts->tv_nsec = timekeeping_get_ns();
@@ -281,7 +284,7 @@ void getnstimeofday(struct timespec *ts)
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

timespec_add_ns(ts, nsecs);
}
@@ -296,7 +299,7 @@ ktime_t ktime_get(void)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
secs = timekeeper.xtime_sec +
timekeeper.wall_to_monotonic.tv_sec;
nsecs = timekeeping_get_ns() +
@@ -304,7 +307,7 @@ ktime_t ktime_get(void)
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));
/*
* Use ktime_set/ktime_add_ns to create a proper ktime on
* 32-bit architectures without CONFIG_KTIME_SCALAR.
@@ -329,14 +332,14 @@ void ktime_get_ts(struct timespec *ts)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
ts->tv_sec = timekeeper.xtime_sec;
ts->tv_nsec = timekeeping_get_ns();
tomono = timekeeper.wall_to_monotonic;
/* If arch requires, add in gettimeoffset() */
ts->tv_nsec += arch_gettimeoffset();

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
ts->tv_nsec + tomono.tv_nsec);
@@ -364,7 +367,7 @@ void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
do {
u32 arch_offset;

- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

*ts_raw = timekeeper.raw_time;
ts_real->tv_sec = timekeeper.xtime_sec;
@@ -378,7 +381,7 @@ void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
nsecs_raw += arch_offset;
nsecs_real += arch_offset;

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

timespec_add_ns(ts_raw, nsecs_raw);
timespec_add_ns(ts_real, nsecs_real);
@@ -417,7 +420,8 @@ int do_settimeofday(const struct timespec *tv)
if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);

timekeeping_forward_now();

@@ -432,7 +436,8 @@ int do_settimeofday(const struct timespec *tv)

timekeeping_update(&timekeeper, true);

- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -456,7 +461,8 @@ int timekeeping_inject_offset(struct timespec *ts)
if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);

timekeeping_forward_now();

@@ -467,7 +473,8 @@ int timekeeping_inject_offset(struct timespec *ts)

timekeeping_update(&timekeeper, true);

- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -539,11 +546,11 @@ void getrawmonotonic(struct timespec *ts)
s64 nsecs;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
nsecs = timekeeping_get_ns_raw();
*ts = timekeeper.raw_time;

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

timespec_add_ns(ts, nsecs);
}
@@ -559,11 +566,11 @@ int timekeeping_valid_for_hres(void)
int ret;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

ret = timekeeper.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

return ret;
}
@@ -576,11 +583,11 @@ u64 timekeeping_max_deferment(void)
unsigned long seq;
u64 ret;
do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

ret = timekeeper.clock->max_idle_ns;

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

return ret;
}
@@ -627,11 +634,13 @@ void __init timekeeping_init(void)
read_persistent_clock(&now);
read_boot_clock(&boot);

- seqlock_init(&timekeeper.lock);
-
+ seqcount_init(&timekeeper.rlock);
+ spin_lock_init(&timekeeper.wlock);
ntp_init();

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);
+
clock = clocksource_default_clock();
if (clock->enable)
clock->enable(clock);
@@ -647,7 +656,10 @@ void __init timekeeping_init(void)
-boot.tv_sec, -boot.tv_nsec);
timekeeper.total_sleep_time.tv_sec = 0;
timekeeper.total_sleep_time.tv_nsec = 0;
- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);
+
}

/* time in seconds when suspend began */
@@ -696,7 +708,8 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
if (!(ts.tv_sec == 0 && ts.tv_nsec == 0))
return;

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);

timekeeping_forward_now();

@@ -704,7 +717,8 @@ void timekeeping_inject_sleeptime(struct timespec *delta)

timekeeping_update(&timekeeper, true);

- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -727,7 +741,8 @@ static void timekeeping_resume(void)

clocksource_resume();

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);

if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
ts = timespec_sub(ts, timekeeping_suspend_time);
@@ -737,7 +752,9 @@ static void timekeeping_resume(void)
timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
timekeeper.ntp_error = 0;
timekeeping_suspended = 0;
- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

touch_softlockup_watchdog();

@@ -755,7 +772,9 @@ static int timekeeping_suspend(void)

read_persistent_clock(&timekeeping_suspend_time);

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);
+
timekeeping_forward_now();
timekeeping_suspended = 1;

@@ -779,7 +798,9 @@ static int timekeeping_suspend(void)
timekeeping_suspend_time =
timespec_add(timekeeping_suspend_time, delta_delta);
}
- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
clocksource_suspend();
@@ -1035,7 +1056,8 @@ static void update_wall_time(void)
unsigned long flags;
s64 remainder;

- write_seqlock_irqsave(&timekeeper.lock, flags);
+ spin_lock_irqsave(&timekeeper.wlock, flags);
+ write_seqcount_begin(&timekeeper.rlock);

/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
@@ -1122,7 +1144,8 @@ static void update_wall_time(void)
timekeeping_update(&timekeeper, false);

out:
- write_sequnlock_irqrestore(&timekeeper.lock, flags);
+ write_seqcount_end(&timekeeper.rlock);
+ spin_unlock_irqrestore(&timekeeper.wlock, flags);

}

@@ -1168,13 +1191,13 @@ void get_monotonic_boottime(struct timespec *ts)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
ts->tv_sec = timekeeper.xtime_sec;
ts->tv_nsec = timekeeping_get_ns();
tomono = timekeeper.wall_to_monotonic;
sleep = timekeeper.total_sleep_time;

- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec + sleep.tv_sec,
ts->tv_nsec + tomono.tv_nsec + sleep.tv_nsec);
@@ -1225,10 +1248,10 @@ struct timespec current_kernel_time(void)
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

now = timekeeper_xtime(&timekeeper);
- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

return now;
}
@@ -1240,11 +1263,11 @@ struct timespec get_monotonic_coarse(void)
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);

now = timekeeper_xtime(&timekeeper);
mono = timekeeper.wall_to_monotonic;
- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
now.tv_nsec + mono.tv_nsec);
@@ -1276,11 +1299,11 @@ void get_xtime_and_monotonic_and_sleep_offset(struct timespec *xtim,
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
*xtim = timekeeper_xtime(&timekeeper);
*wtom = timekeeper.wall_to_monotonic;
*sleep = timekeeper.total_sleep_time;
- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));
}

/**
@@ -1292,9 +1315,9 @@ ktime_t ktime_get_monotonic_offset(void)
struct timespec wtom;

do {
- seq = read_seqbegin(&timekeeper.lock);
+ seq = read_seqcount_begin(&timekeeper.rlock);
wtom = timekeeper.wall_to_monotonic;
- } while (read_seqretry(&timekeeper.lock, seq));
+ } while (read_seqcount_retry(&timekeeper.rlock, seq));

return timespec_to_ktime(wtom);
}
--
1.7.3.2.146.gca209


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