[PATCH 0/3] clocksource: CLOCK_MONOTONIC_RAW - Kernel

This is a discussion on [PATCH 0/3] clocksource: CLOCK_MONOTONIC_RAW - Kernel ; Hi, This is a resend of the raw monotonic clock patches. Compared to the original patches I inserted a cleanup patch inbetween to keep the last patch simple and to avoid the rounding issues, I dropped the fraction completely, so ...

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Thread: [PATCH 0/3] clocksource: CLOCK_MONOTONIC_RAW

  1. [PATCH 0/3] clocksource: CLOCK_MONOTONIC_RAW

    Hi,

    This is a resend of the raw monotonic clock patches. Compared to the
    original patches I inserted a cleanup patch inbetween to keep the last
    patch simple and to avoid the rounding issues, I dropped the fraction
    completely, so that it becomes even simpler.

    bye, Roman

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  2. [PATCH 2/3] clocksource: introduce clocksource_forward_now()

    To keep the raw monotonic patch simple first introduce
    clocksource_forward_now(), which takes care of the offset since the last
    update_wall_time() call and adds it to the clock, so there is no need
    anymore to deal with it explicitly at various places, which need to make
    significant changes to the clock.
    This is also gets rid of the timekeeping_suspend_nsecs, instead of
    waiting until resume, the value is accumulated during suspend. In the end
    there is only a single user of __get_nsec_offset() left, so I integrated
    it back to getnstimeofday().

    Signed-off-by: Roman Zippel

    ---
    kernel/time/timekeeping.c | 71 +++++++++++++++++++++-------------------------
    1 file changed, 33 insertions(+), 38 deletions(-)

    Index: linux-2.6/kernel/time/timekeeping.c
    ================================================== =================
    --- linux-2.6.orig/kernel/time/timekeeping.c
    +++ linux-2.6/kernel/time/timekeeping.c
    @@ -58,27 +58,23 @@ struct clocksource *clock;

    #ifdef CONFIG_GENERIC_TIME
    /**
    - * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
    + * clocksource_forward_now - update clock to the current time
    *
    - * private function, must hold xtime_lock lock when being
    - * called. Returns the number of nanoseconds since the
    - * last call to update_wall_time() (adjusted by NTP scaling)
    + * Forward the current clock to update its state since the last call to
    + * update_wall_time(). This is useful before significant clock changes,
    + * as it avoids having to deal with this time offset explicitly.
    */
    -static inline s64 __get_nsec_offset(void)
    +static void clocksource_forward_now(void)
    {
    cycle_t cycle_now, cycle_delta;
    - s64 ns_offset;
    + s64 nsec;

    - /* 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;
    + clock->cycle_last = cycle_now;

    - /* convert to nanoseconds: */
    - ns_offset = cyc2ns(clock, cycle_delta);
    -
    - return ns_offset;
    + nsec = cyc2ns(clock, cycle_delta);
    + timespec_add_ns(&xtime, nsec);
    }

    /**
    @@ -89,6 +85,7 @@ static inline s64 __get_nsec_offset(void
    */
    void getnstimeofday(struct timespec *ts)
    {
    + cycle_t cycle_now, cycle_delta;
    unsigned long seq;
    s64 nsecs;

    @@ -96,7 +93,15 @@ void getnstimeofday(struct timespec *ts)
    seq = read_seqbegin(&xtime_lock);

    *ts = xtime;
    - nsecs = __get_nsec_offset();
    +
    + /* 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 = cyc2ns(clock, cycle_delta);

    } while (read_seqretry(&xtime_lock, seq));

    @@ -129,22 +134,22 @@ EXPORT_SYMBOL(do_gettimeofday);
    */
    int do_settimeofday(struct timespec *tv)
    {
    + struct timespec ts_delta;
    unsigned long flags;
    - time_t wtm_sec, sec = tv->tv_sec;
    - long wtm_nsec, nsec = tv->tv_nsec;

    if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
    return -EINVAL;

    write_seqlock_irqsave(&xtime_lock, flags);

    - nsec -= __get_nsec_offset();
    + clocksource_forward_now();
    +
    + ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
    + ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
    + wall_to_monotonic = timespec_sub(wall_to_monotonic, ts_delta);

    - wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
    - wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
    + xtime = *tv;

    - set_normalized_timespec(&xtime, sec, nsec);
    - set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
    update_xtime_cache(0);

    clock->error = 0;
    @@ -170,22 +175,17 @@ EXPORT_SYMBOL(do_settimeofday);
    static void change_clocksource(void)
    {
    struct clocksource *new;
    - cycle_t now;
    - u64 nsec;

    new = clocksource_get_next();

    if (clock == new)
    return;

    - new->cycle_last = 0;
    - now = clocksource_read(new);
    - nsec = __get_nsec_offset();
    - timespec_add_ns(&xtime, nsec);
    + clocksource_forward_now();

    clock = new;
    - clock->cycle_last = now;
    -
    + clock->cycle_last = 0;
    + clock->cycle_last = clocksource_read(new);
    clock->error = 0;
    clock->xtime_nsec = 0;
    clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
    @@ -200,8 +200,8 @@ static void change_clocksource(void)
    */
    }
    #else
    +static inline void clocksource_forward_now(void) { }
    static inline void change_clocksource(void) { }
    -static inline s64 __get_nsec_offset(void) { return 0; }
    #endif

    /**
    @@ -265,8 +265,6 @@ void __init timekeeping_init(void)
    static int timekeeping_suspended;
    /* time in seconds when suspend began */
    static unsigned long timekeeping_suspend_time;
    -/* xtime offset when we went into suspend */
    -static s64 timekeeping_suspend_nsecs;

    /**
    * timekeeping_resume - Resumes the generic timekeeping subsystem.
    @@ -292,8 +290,6 @@ static int timekeeping_resume(struct sys
    wall_to_monotonic.tv_sec -= sleep_length;
    total_sleep_time += sleep_length;
    }
    - /* Make sure that we have the correct xtime reference */
    - timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
    update_xtime_cache(0);
    /* re-base the last cycle value */
    clock->cycle_last = 0;
    @@ -319,8 +315,7 @@ static int timekeeping_suspend(struct sy
    timekeeping_suspend_time = read_persistent_clock();

    write_seqlock_irqsave(&xtime_lock, flags);
    - /* Get the current xtime offset */
    - timekeeping_suspend_nsecs = __get_nsec_offset();
    + clocksource_forward_now();
    timekeeping_suspended = 1;
    write_sequnlock_irqrestore(&xtime_lock, flags);

    @@ -461,10 +456,10 @@ void update_wall_time(void)
    */
    while (offset >= clock->cycle_interval) {
    /* accumulate one interval */
    - clock->xtime_nsec += clock->xtime_interval;
    - clock->cycle_last += clock->cycle_interval;
    offset -= clock->cycle_interval;
    + clock->cycle_last += clock->cycle_interval;

    + clock->xtime_nsec += clock->xtime_interval;
    if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
    clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
    xtime.tv_sec++;

    --

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