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In tc_windup, handle the case where the previous call to tc_windup was

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more than 1s earlier.  Prior to this commit, the computation of
th_scale * delta (which produces a 64-bit value equal to the time since
the last tc_windup call in units of 2^(-64) seconds) would overflow and
any complete seconds would be lost.

We fix this by repeatedly converting tc_frequency units of timecounter
to one seconds; this is not exactly correct, since it loses the NTP
adjustment, but if we find ourselves going more than 1s at a time between
clock interrupts, losing a few seconds worth of NTP adjustments is the
least of our problems...
This commit is contained in:
Colin Percival 2010-11-22 09:13:25 +00:00
parent bb63fdde6d
commit aa519c0a64
1 changed files with 10 additions and 0 deletions
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10
sys/kern/kern_tc.c
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@ -442,6 +442,16 @@ tc_windup(void)
ncount = 0;
th->th_offset_count += delta;
th->th_offset_count &= th->th_counter->tc_counter_mask;
while (delta > th->th_counter->tc_frequency) {
/* Eat complete unadjusted seconds. */
delta -= th->th_counter->tc_frequency;
th->th_offset.sec++;
}
if ((delta > th->th_counter->tc_frequency / 2) &&
(th->th_scale * delta < (uint64_t)1 << 63)) {
/* The product th_scale * delta just barely overflows. */
th->th_offset.sec++;
}
bintime_addx(&th->th_offset, th->th_scale * delta);
/*