Messages in this thread Patch in this message | | | From | John Stultz <> | Subject | [PATCH 3/7] time: Split timekeeper lock into separate reader/writer locks | Date | Mon, 27 Feb 2012 16:29:30 -0800 |
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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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