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timekeeping: Introduce read_boot_clock

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Add the new function read_boot_clock to get the exact time the system
has been started. For architectures without support for exact boot
time a new weak function is added that returns 0.  Use the exact boot
time to initialize wall_to_monotonic, or xtime if the read_boot_clock
returned 0.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134811.296703241@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-08-14 15:47:32 +02:00 committed by Thomas Gleixner
parent d4f587c67f
commit 23970e389e
3 changed files with 28 additions and 14 deletions
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17
arch/s390/kernel/time.c
View file

@ -187,6 +187,11 @@ void read_persistent_clock(struct timespec *ts)
tod_to_timeval(get_clock() - TOD_UNIX_EPOCH, ts);
}
void read_boot_clock(struct timespec *ts)
{
tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, ts);
}
static cycle_t read_tod_clock(struct clocksource *cs)
{
return get_clock();
@ -243,9 +248,6 @@ void update_vsyscall_tz(void)
*/
void __init time_init(void)
{
struct timespec ts;
unsigned long flags;
/* Reset time synchronization interfaces. */
etr_reset();
stp_reset();
@ -261,15 +263,6 @@ void __init time_init(void)
if (clocksource_register(&clocksource_tod) != 0)
panic("Could not register TOD clock source");
/*
* Reset wall_to_monotonic to the initial timestamp created
* in head.S to get a precise value in /proc/uptime.
*/
write_seqlock_irqsave(&xtime_lock, flags);
tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, &ts);
set_normalized_timespec(&wall_to_monotonic, -ts.tv_sec, -ts.tv_nsec);
write_sequnlock_irqrestore(&xtime_lock, flags);
/* Enable TOD clock interrupts on the boot cpu. */
init_cpu_timer();

1
include/linux/time.h
View file

@ -102,6 +102,7 @@ extern struct timespec wall_to_monotonic;
extern seqlock_t xtime_lock;
extern void read_persistent_clock(struct timespec *ts);
extern void read_boot_clock(struct timespec *ts);
extern int update_persistent_clock(struct timespec now);
extern int no_sync_cmos_clock __read_mostly;
void timekeeping_init(void);

24
kernel/time/timekeeping.c
View file

@ -501,6 +501,21 @@ void __attribute__((weak)) read_persistent_clock(struct timespec *ts)
ts->tv_nsec = 0;
}
/**
* read_boot_clock - Return time of the system start.
*
* Weak dummy function for arches that do not yet support it.
* Function to read the exact time the system has been started.
* Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
*
* XXX - Do be sure to remove it once all arches implement it.
*/
void __attribute__((weak)) read_boot_clock(struct timespec *ts)
{
ts->tv_sec = 0;
ts->tv_nsec = 0;
}
/*
* timekeeping_init - Initializes the clocksource and common timekeeping values
*/
@ -508,9 +523,10 @@ void __init timekeeping_init(void)
{
struct clocksource *clock;
unsigned long flags;
struct timespec now;
struct timespec now, boot;
read_persistent_clock(&now);
read_boot_clock(&boot);
write_seqlock_irqsave(&xtime_lock, flags);
@ -525,8 +541,12 @@ void __init timekeeping_init(void)
xtime.tv_nsec = now.tv_nsec;
raw_time.tv_sec = 0;
raw_time.tv_nsec = 0;
if (boot.tv_sec == 0 && boot.tv_nsec == 0) {
boot.tv_sec = xtime.tv_sec;
boot.tv_nsec = xtime.tv_nsec;
}
set_normalized_timespec(&wall_to_monotonic,
-xtime.tv_sec, -xtime.tv_nsec);
-boot.tv_sec, -boot.tv_nsec);
update_xtime_cache(0);
total_sleep_time.tv_sec = 0;
total_sleep_time.tv_nsec = 0;