Author: cperciva
Date: Mon Nov 22 09:13:25 2010
New Revision: 215665
URL: http://svn.freebsd.org/changeset/base/215665
Log:
In tc_windup, handle the case where the previous call to tc_windup was
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...
Modified:
head/sys/kern/kern_tc.c
Modified: head/sys/kern/kern_tc.c
==============================================================================
--- head/sys/kern/kern_tc.c Mon Nov 22 09:06:59 2010 (r215664)
+++ head/sys/kern/kern_tc.c Mon Nov 22 09:13:25 2010 (r215665)
@@ -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);
/*
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