time: apply NTP frequency/tick changes immediately

Since the GENERIC_TIME changes landed, the adjtimex behavior changed
for struct timex.tick and .freq changed. When the tick or freq value
is set, we adjust the tick_length_base in ntp_update_frequency().
However, this new value doesn't get applied to tick_length until the
next second (via second_overflow).

This means some applications that do quick time tweaking do not see the
requested change made as quickly as expected.

I've run a few tests with this change, and ntpd still functions fine.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index f5f793d92415..e1fa3689a903 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -51,6 +51,7 @@ static long ntp_tick_adj;
 
 static void ntp_update_frequency(void)
 {
+        u64 old_tick_length_base = tick_length_base;
         u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
                                 << NTP_SCALE_SHIFT;
         second_length += (s64)ntp_tick_adj << NTP_SCALE_SHIFT;
@@ -60,6 +61,12 @@ static void ntp_update_frequency(void)
 
         tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
         tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
+
+        /*
+         * Don't wait for the next second_overflow, apply
+         * the change to the tick length immediately
+         */
+        tick_length += tick_length_base - old_tick_length_base;
 }
 
 static void ntp_update_offset(long offset)