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time: ntp: fix bug in ntp_update_offset() & do_adjtimex()

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Impact: change (fix) the way the NTP PLL seconds offset is initialized/tracked

Fix a bug and do a micro-optimization:

When PLL is enabled we do not reset time_reftime. If the PLL
was off for a long time (for example after bootup), this is
arguably the wrong thing to do.

We already had a hack for the common boot-time case in
ntp_update_offset(), in form of:

	if (unlikely(time_status & STA_FREQHOLD || time_reftime == 0))
 		secs = 0;

But the update delta should be reset later on too - not just when
the PLL is enabled for the first time after bootup.

So do it on !STA_PLL -> STA_PLL transitions.

This changes behavior, as previously if ntpd was disabled for
a long time and we restarted it, we'd run from that last update,
with a very large delta.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar
2009-02-22 13:38:40 +01:00
parent c7986acba2
commit 10dd31a7a1
1 changed files with 8 additions and 1 deletions
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9
kernel/time/ntp.c
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@@ -142,7 +142,7 @@ static void ntp_update_offset(long offset)
* and in which mode (PLL or FLL). * and in which mode (PLL or FLL).
*/ */
secs = xtime.tv_sec - time_reftime; secs = xtime.tv_sec - time_reftime;
if (unlikely(time_status & STA_FREQHOLD || time_reftime == 0)) if (unlikely(time_status & STA_FREQHOLD))
secs = 0; secs = 0;
time_reftime = xtime.tv_sec; time_reftime = xtime.tv_sec;
@@ -394,6 +394,13 @@ int do_adjtimex(struct timex *txc)
} }
/* only set allowed bits */ /* only set allowed bits */
time_status &= STA_RONLY; time_status &= STA_RONLY;
/*
* If we turn on PLL adjustments then reset the
* reference time to current time.
*/
if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
time_reftime = xtime.tv_sec;
time_status |= txc->status & ~STA_RONLY; time_status |= txc->status & ~STA_RONLY;
switch (time_state) { switch (time_state) {