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>
---
kernel/time/timekeeping.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 49cbceef5deb..6922dae7317c 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2047,10 +2047,6 @@ void update_wall_time(void)
tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
#endif
- /* Check if there's really nothing to do */
- if (offset < real_tk->cycle_interval)
- goto out;
-
/* Do some additional sanity checking */
timekeeping_check_update(tk, offset);
@@ -2332,6 +2328,10 @@ 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))
+ update_wall_time();
+
if (tai != orig_tai)
clock_was_set();
--
2.14.3
