When the NTP frequency is set directly from userspace using the ADJ_FREQUENCY or ADJ_TICK timex mode, immediately update the timekeeper's multiplier instead of waiting for the next tick.
This removes a hidden non-deterministic delay in setting of the frequency and allows an extremely tight control of the system clock with update rates close to or even exceeding the kernel HZ. Cc: Thomas Gleixner <t...@linutronix.de> Cc: John Stultz <john.stu...@linaro.org> Cc: Richard Cochran <richardcoch...@gmail.com> Cc: Prarit Bhargava <pra...@redhat.com> Signed-off-by: Miroslav Lichvar <mlich...@redhat.com> --- Notes: RFC->v1: - added a new parameter to force the update of the timekeeper to the current NTP tick length only from adjtimex() - added timekeeping_advance() to keep the parameter local to timekeeping.c kernel/time/timekeeping.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 49cbceef5deb..5524c07d43e3 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -2021,11 +2021,11 @@ static u64 logarithmic_accumulation(struct timekeeper *tk, u64 offset, return offset; } -/** - * update_wall_time - Uses the current clocksource to increment the wall time - * +/* + * timekeeping_advance - Updates the timekeeper to the current time and + * current NTP tick length */ -void update_wall_time(void) +static void timekeeping_advance(bool force_update) { struct timekeeper *real_tk = &tk_core.timekeeper; struct timekeeper *tk = &shadow_timekeeper; @@ -2048,7 +2048,7 @@ void update_wall_time(void) #endif /* Check if there's really nothing to do */ - if (offset < real_tk->cycle_interval) + if (offset < real_tk->cycle_interval && !force_update) goto out; /* Do some additional sanity checking */ @@ -2105,6 +2105,15 @@ void update_wall_time(void) clock_was_set_delayed(); } +/** + * update_wall_time - Uses the current clocksource to increment the wall time + * + */ +void update_wall_time(void) +{ + timekeeping_advance(false); +} + /** * getboottime64 - Return the real time of system boot. * @ts: pointer to the timespec64 to be set @@ -2332,6 +2341,10 @@ int do_adjtimex(struct timex *txc) write_seqcount_end(&tk_core.seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + /* Update the multiplier immediately if frequency was set directly */ + if (txc->modes & (ADJ_FREQUENCY | ADJ_TICK)) + timekeeping_advance(true); + if (tai != orig_tai) clock_was_set(); -- 2.14.3