Messages in this thread Patch in this message | | | Date | Wed, 2 Apr 2008 13:50:36 +0200 (CEST) | From | Roman Zippel <> | Subject | Re: [PATCH 2/2] Introduce CLOCK_MONOTONIC_RAW |
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Hi,
On Tue, 18 Mar 2008, john stultz wrote:
> My solution is to introduce CLOCK_MONOTONIC_RAW. This exposes a > nanosecond based time value, that increments starting at bootup and has > no frequency adjustments made to it what so ever. > > The time is accessed from userspace via the posix_clock_gettime() > syscall, passing CLOCK_MONOTONIC_RAW as the clock_id.
This is a reworked version of this patch based on the previous clocksource_forward_now patch, since clocksource_forward_now() takes care of the time offset now, it's not needed to do this at various places. I also got rid of the monotonic_raw splitting, so the work done during update_wall_time() is quite a bit simpler.
bye, Roman
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
--- include/linux/clocksource.h | 5 ++++ include/linux/time.h | 2 + kernel/posix-timers.c | 15 ++++++++++++++ kernel/time/timekeeping.c | 47 ++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 69 insertions(+)
Index: linux-2.6/include/linux/clocksource.h =================================================================== --- linux-2.6.orig/include/linux/clocksource.h +++ linux-2.6/include/linux/clocksource.h @@ -79,6 +79,7 @@ struct clocksource { /* timekeeping specific data, ignore */ cycle_t cycle_interval; u64 xtime_interval; + u64 raw_interval; /* * Second part is written at each timer interrupt * Keep it in a different cache line to dirty no @@ -87,6 +88,8 @@ struct clocksource { cycle_t cycle_last ____cacheline_aligned_in_smp; u64 xtime_nsec; s64 error; + u64 raw_nsec; + long raw_sec; #ifdef CONFIG_CLOCKSOURCE_WATCHDOG /* Watchdog related data, used by the framework */ @@ -215,6 +218,8 @@ static inline void clocksource_calculate /* Go back from cycles -> shifted ns, this time use ntp adjused mult */ c->xtime_interval = (u64)c->cycle_interval * c->mult; + c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) << + (NTP_SCALE_SHIFT - c->shift); } Index: linux-2.6/include/linux/time.h =================================================================== --- linux-2.6.orig/include/linux/time.h +++ linux-2.6/include/linux/time.h @@ -116,6 +116,7 @@ extern int do_setitimer(int which, struc extern unsigned int alarm_setitimer(unsigned int seconds); extern int do_getitimer(int which, struct itimerval *value); extern void getnstimeofday(struct timespec *tv); +extern void getrawmonotonic(struct timespec *ts); extern void getboottime(struct timespec *ts); extern void monotonic_to_bootbased(struct timespec *ts); @@ -218,6 +219,7 @@ struct itimerval { #define CLOCK_MONOTONIC 1 #define CLOCK_PROCESS_CPUTIME_ID 2 #define CLOCK_THREAD_CPUTIME_ID 3 +#define CLOCK_MONOTONIC_RAW 4 /* * The IDs of various hardware clocks: Index: linux-2.6/kernel/posix-timers.c =================================================================== --- linux-2.6.orig/kernel/posix-timers.c +++ linux-2.6/kernel/posix-timers.c @@ -224,6 +224,15 @@ static int posix_ktime_get_ts(clockid_t } /* + * Get monotonic time for posix timers + */ +static int posix_get_monotonic_raw(clockid_t which_clock, struct timespec *tp) +{ + getrawmonotonic(tp); + return 0; +} + +/* * Initialize everything, well, just everything in Posix clocks/timers ;) */ static __init int init_posix_timers(void) @@ -236,9 +245,15 @@ static __init int init_posix_timers(void .clock_get = posix_ktime_get_ts, .clock_set = do_posix_clock_nosettime, }; + struct k_clock clock_monotonic_raw = { + .clock_getres = hrtimer_get_res, + .clock_get = posix_get_monotonic_raw, + .clock_set = do_posix_clock_nosettime, + }; register_posix_clock(CLOCK_REALTIME, &clock_realtime); register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic); + register_posix_clock(CLOCK_MONOTONIC_RAW, &clock_monotonic_raw); posix_timers_cache = kmem_cache_create("posix_timers_cache", sizeof (struct k_itimer), 0, SLAB_PANIC, Index: linux-2.6/kernel/time/timekeeping.c =================================================================== --- linux-2.6.orig/kernel/time/timekeeping.c +++ linux-2.6/kernel/time/timekeeping.c @@ -75,6 +75,10 @@ static void clocksource_forward_now(void nsec = cyc2ns(clock, cycle_delta); timespec_add_ns(&xtime, nsec); + + nsec = ((s64)cycle_delta * clock->mult_orig) << + (NTP_SCALE_SHIFT - clock->shift); + clock->raw_nsec += nsec; } /** @@ -181,6 +185,9 @@ static void change_clocksource(void) clocksource_forward_now(); + new->raw_sec = clock->raw_sec; + new->raw_nsec = clock->raw_nsec; + clock = new; clock->cycle_last = clocksource_read(new); clock->error = 0; @@ -202,6 +209,40 @@ static inline void change_clocksource(vo #endif /** + * getrawmonotonic - Returns the raw monotonic time in a timespec + * @ts: pointer to the timespec to be set + * + * Returns the raw monotonic time (completely un-modified by ntp) + */ +void getrawmonotonic(struct timespec *ts) +{ + unsigned long seq; + s64 nsecs; + cycle_t cycle_now, cycle_delta; + + do { + seq = read_seqbegin(&xtime_lock); + + /* read clocksource: */ + cycle_now = clocksource_read(clock); + + /* calculate the delta since the last update_wall_time: */ + cycle_delta = (cycle_now - clock->cycle_last) & clock->mask; + + /* convert to nanoseconds: */ + nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift; + + ts->tv_sec = clock->raw_sec; + ts->tv_nsec = clock->raw_nsec >> NTP_SCALE_SHIFT; + + } while (read_seqretry(&xtime_lock, seq)); + + timespec_add_ns(ts, nsecs); +} +EXPORT_SYMBOL(getrawmonotonic); + + +/** * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres */ int timekeeping_valid_for_hres(void) @@ -462,6 +503,12 @@ void update_wall_time(void) second_overflow(); } + clock->raw_nsec += clock->raw_interval; + if ((u32)(clock->raw_nsec >> NTP_SCALE_SHIFT) >= NSEC_PER_SEC) { + clock->raw_nsec -= (u64)NSEC_PER_SEC << NTP_SCALE_SHIFT; + clock->raw_sec++; + } + /* accumulate error between NTP and clock interval */ clock->error += tick_length; clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
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