[RFC patch 4/8] timekeeping: Split timekeeper_lock into lock andseqcount

From: Thomas Gleixner
Date: Thu Feb 21 2013 - 17:51:45 EST

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In reply to: Thomas Gleixner: "[RFC patch 0/8] timekeeping: Implement shadow timekeeper to shortenin kernel reader side blocking"
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We want to shorten the seqcount write hold time. So split the seqlock
into a lock and a seqcount.

Open code the seqwrite_lock in the places which matter and drop the
sequence counter update where it's pointless.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/time/timekeeping.c | 118 +++++++++++++++++++++++++---------------------
1 file changed, 65 insertions(+), 53 deletions(-)

Index: linux-2.6/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.orig/kernel/time/timekeeping.c
+++ linux-2.6/kernel/time/timekeeping.c
@@ -26,7 +26,8 @@
#include "tick-internal.h"

static struct timekeeper timekeeper;
-static DEFINE_SEQLOCK(timekeeper_lock);
+static DEFINE_RAW_SPINLOCK(timekeeper_lock);
+static seqcount_t timekeeper_seq;

/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@@ -189,8 +190,6 @@ static void update_pvclock_gtod(struct t

/**
* pvclock_gtod_register_notifier - register a pvclock timedata update listener
- *
- * Must hold write on timekeeper.lock
*/
int pvclock_gtod_register_notifier(struct notifier_block *nb)
{
@@ -198,11 +197,10 @@ int pvclock_gtod_register_notifier(struc
unsigned long flags;
int ret;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
ret = raw_notifier_chain_register(&pvclock_gtod_chain, nb);
- /* update timekeeping data */
update_pvclock_gtod(tk);
- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

return ret;
}
@@ -211,23 +209,21 @@ EXPORT_SYMBOL_GPL(pvclock_gtod_register_
/**
* pvclock_gtod_unregister_notifier - unregister a pvclock
* timedata update listener
- *
- * Must hold write on timekeeper.lock
*/
int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
{
unsigned long flags;
int ret;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
ret = raw_notifier_chain_unregister(&pvclock_gtod_chain, nb);
- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

return ret;
}
EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);

-/* must hold write on timekeeper.lock */
+/* must hold timekeeper_lock */
static void timekeeping_update(struct timekeeper *tk, bool clearntp)
{
if (clearntp) {
@@ -281,12 +277,12 @@ int __getnstimeofday(struct timespec *ts
s64 nsecs = 0;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

ts->tv_sec = tk->xtime_sec;
nsecs = timekeeping_get_ns(tk);

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

ts->tv_nsec = 0;
timespec_add_ns(ts, nsecs);
@@ -322,11 +318,11 @@ ktime_t ktime_get(void)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
secs = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
nsecs = timekeeping_get_ns(tk) + tk->wall_to_monotonic.tv_nsec;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));
/*
* Use ktime_set/ktime_add_ns to create a proper ktime on
* 32-bit architectures without CONFIG_KTIME_SCALAR.
@@ -353,12 +349,12 @@ void ktime_get_ts(struct timespec *ts)
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
ts->tv_sec = tk->xtime_sec;
nsec = timekeeping_get_ns(tk);
tomono = tk->wall_to_monotonic;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

ts->tv_sec += tomono.tv_sec;
ts->tv_nsec = 0;
@@ -386,7 +382,7 @@ void getnstime_raw_and_real(struct times
WARN_ON_ONCE(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

*ts_raw = tk->raw_time;
ts_real->tv_sec = tk->xtime_sec;
@@ -395,7 +391,7 @@ void getnstime_raw_and_real(struct times
nsecs_raw = timekeeping_get_ns_raw(tk);
nsecs_real = timekeeping_get_ns(tk);

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

timespec_add_ns(ts_raw, nsecs_raw);
timespec_add_ns(ts_real, nsecs_real);
@@ -435,7 +431,8 @@ int do_settimeofday(const struct timespe
if (!timespec_valid_strict(tv))
return -EINVAL;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

timekeeping_forward_now(tk);

@@ -449,7 +446,8 @@ int do_settimeofday(const struct timespe

timekeeping_update(tk, true);

- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -474,7 +472,8 @@ int timekeeping_inject_offset(struct tim
if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

timekeeping_forward_now(tk);

@@ -491,7 +490,8 @@ int timekeeping_inject_offset(struct tim
error: /* even if we error out, we forwarded the time, so call update */
timekeeping_update(tk, true);

- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -513,7 +513,8 @@ static int change_clocksource(void *data

new = (struct clocksource *) data;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

timekeeping_forward_now(tk);
if (!new->enable || new->enable(new) == 0) {
@@ -524,7 +525,8 @@ static int change_clocksource(void *data
}
timekeeping_update(tk, true);

- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

return 0;
}
@@ -574,11 +576,11 @@ void getrawmonotonic(struct timespec *ts
s64 nsecs;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
nsecs = timekeeping_get_ns_raw(tk);
*ts = tk->raw_time;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

timespec_add_ns(ts, nsecs);
}
@@ -594,11 +596,11 @@ int timekeeping_valid_for_hres(void)
int ret;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

ret = tk->clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

return ret;
}
@@ -613,11 +615,11 @@ u64 timekeeping_max_deferment(void)
u64 ret;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

ret = tk->clock->max_idle_ns;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

return ret;
}
@@ -682,7 +684,8 @@ void __init timekeeping_init(void)

ntp_init();

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);
clock = clocksource_default_clock();
if (clock->enable)
clock->enable(clock);
@@ -701,7 +704,8 @@ void __init timekeeping_init(void)
tmp.tv_nsec = 0;
tk_set_sleep_time(tk, tmp);

- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}

/* time in seconds when suspend began */
@@ -749,7 +753,8 @@ void timekeeping_inject_sleeptime(struct
if (has_persistent_clock())
return;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

timekeeping_forward_now(tk);

@@ -757,7 +762,8 @@ void timekeeping_inject_sleeptime(struct

timekeeping_update(tk, true);

- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

/* signal hrtimers about time change */
clock_was_set();
@@ -781,7 +787,8 @@ static void timekeeping_resume(void)
clockevents_resume();
clocksource_resume();

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
ts = timespec_sub(ts, timekeeping_suspend_time);
@@ -792,7 +799,8 @@ static void timekeeping_resume(void)
tk->ntp_error = 0;
timekeeping_suspended = 0;
timekeeping_update(tk, false);
- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

touch_softlockup_watchdog();

@@ -811,7 +819,8 @@ static int timekeeping_suspend(void)

read_persistent_clock(&timekeeping_suspend_time);

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);
timekeeping_forward_now(tk);
timekeeping_suspended = 1;

@@ -834,7 +843,8 @@ 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_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
clocksource_suspend();
@@ -1172,7 +1182,8 @@ static void update_wall_time(void)
int shift = 0, maxshift;
unsigned long flags;

- write_seqlock_irqsave(&timekeeper_lock, flags);
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ write_seqcount_begin(&timekeeper_seq);

/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
@@ -1227,7 +1238,8 @@ static void update_wall_time(void)
timekeeping_update(tk, false);

out:
- write_sequnlock_irqrestore(&timekeeper_lock, flags);
+ write_seqcount_end(&timekeeper_seq);
+ raw_spin_unlock_irqrestore(&timekeeper_lock, flags);

}

@@ -1275,13 +1287,13 @@ void get_monotonic_boottime(struct times
WARN_ON(timekeeping_suspended);

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
ts->tv_sec = tk->xtime_sec;
nsec = timekeeping_get_ns(tk);
tomono = tk->wall_to_monotonic;
sleep = tk->total_sleep_time;

- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

ts->tv_sec += tomono.tv_sec + sleep.tv_sec;
ts->tv_nsec = 0;
@@ -1340,10 +1352,10 @@ struct timespec current_kernel_time(void
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

now = tk_xtime(tk);
- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

return now;
}
@@ -1356,11 +1368,11 @@ struct timespec get_monotonic_coarse(voi
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

now = tk_xtime(tk);
mono = tk->wall_to_monotonic;
- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
now.tv_nsec + mono.tv_nsec);
@@ -1391,11 +1403,11 @@ void get_xtime_and_monotonic_and_sleep_o
unsigned long seq;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
*xtim = tk_xtime(tk);
*wtom = tk->wall_to_monotonic;
*sleep = tk->total_sleep_time;
- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));
}

#ifdef CONFIG_HIGH_RES_TIMERS
@@ -1415,14 +1427,14 @@ ktime_t ktime_get_update_offsets(ktime_t
u64 secs, nsecs;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);

secs = tk->xtime_sec;
nsecs = timekeeping_get_ns(tk);

*offs_real = tk->offs_real;
*offs_boot = tk->offs_boot;
- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

now = ktime_add_ns(ktime_set(secs, 0), nsecs);
now = ktime_sub(now, *offs_real);
@@ -1440,9 +1452,9 @@ ktime_t ktime_get_monotonic_offset(void)
struct timespec wtom;

do {
- seq = read_seqbegin(&timekeeper_lock);
+ seq = read_seqcount_begin(&timekeeper_seq);
wtom = tk->wall_to_monotonic;
- } while (read_seqretry(&timekeeper_lock, seq));
+ } while (read_seqcount_retry(&timekeeper_seq, seq));

return timespec_to_ktime(wtom);
}

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Next message: Thomas Gleixner: "[RFC patch 2/8] timekeeping: Make jiffies_lock internal"
Previous message: Rafael J. Wysocki: "Re: [Update 2][PATCH 2/7] ACPI / scan: Introduce common code for ACPI-based device hotplug"
In reply to: Thomas Gleixner: "[RFC patch 0/8] timekeeping: Implement shadow timekeeper to shortenin kernel reader side blocking"
Next in thread: Thomas Gleixner: "[RFC patch 2/8] timekeeping: Make jiffies_lock internal"
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