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authorcperciva <cperciva@FreeBSD.org>2010-11-22 09:13:25 +0000
committercperciva <cperciva@FreeBSD.org>2010-11-22 09:13:25 +0000
commit6cdc82f90731dd5c361708b204ef977079a6a146 (patch)
tree7eeada262b358d7d01b66418e625a174d131b1a4
parent46e50a7603917cf17df6f85004e94e846f192e37 (diff)
downloadFreeBSD-src-6cdc82f90731dd5c361708b204ef977079a6a146.zip
FreeBSD-src-6cdc82f90731dd5c361708b204ef977079a6a146.tar.gz
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...
-rw-r--r--sys/kern/kern_tc.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 3e8d470..2487b6b 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -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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