Author: markj
Date: Fri Mar 3 20:57:40 2017
New Revision: 314625
URL: https://svnweb.freebsd.org/changeset/base/314625
Log:
Fix a ticks comparison in sched_pctcpu_update().
We may fail to reset the %CPU tracking window if a thread does not run
for over half of the ticks rollover period, resulting in a bogus %CPU
value for the thread until ticks fully rolls over. Handle this by comparing
the unsigned difference ticks - ts_ltick with SCHED_TICK_TARG instead.
Reviewed by: cem, jeff
MFC after: 1 week
Sponsored by: Dell EMC Isilon
Modified:
head/sys/kern/sched_ule.c
Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c Fri Mar 3 20:51:57 2017 (r314624)
+++ head/sys/kern/sched_ule.c Fri Mar 3 20:57:40 2017 (r314625)
@@ -1662,7 +1662,11 @@ sched_pctcpu_update(struct td_sched *ts,
{
int t = ticks;
- if (t - ts->ts_ltick >= SCHED_TICK_TARG) {
+ /*
+ * The signed difference may be negative if the thread hasn't run for
+ * over half of the ticks rollover period.
+ */
+ if ((u_int)(t - ts->ts_ltick) >= SCHED_TICK_TARG) {
ts->ts_ticks = 0;
ts->ts_ftick = t - SCHED_TICK_TARG;
} else if (t - ts->ts_ftick >= SCHED_TICK_MAX) {
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