Author: luigi
Date: Sun Mar 7 14:29:12 2010
New Revision: 204831
URL: http://svn.freebsd.org/changeset/base/204831
Log:
MFC r197137 and r200510, which fixes a problem in 8.0
with callouts firing one tick too late. See the logs for
the original patch for details.
RELENG_7 is not affected by the problem.
Modified:
stable/8/sys/kern/kern_timeout.c
Modified: stable/8/sys/kern/kern_timeout.c
==============================================================================
--- stable/8/sys/kern/kern_timeout.c Sun Mar 7 14:23:44 2010
(r204830)
+++ stable/8/sys/kern/kern_timeout.c Sun Mar 7 14:29:12 2010
(r204831)
@@ -82,6 +82,23 @@ SYSCTL_INT(_debug, OID_AUTO, to_avg_mpca
*/
int callwheelsize, callwheelbits, callwheelmask;
+/*
+ * There is one struct callout_cpu per cpu, holding all relevant
+ * state for the callout processing thread on the individual CPU.
+ * In particular:
+ * cc_ticks is incremented once per tick in callout_cpu().
+ * It tracks the global 'ticks' but in a way that the individual
+ * threads should not worry about races in the order in which
+ * hardclock() and hardclock_cpu() run on the various CPUs.
+ * cc_softclock is advanced in callout_cpu() to point to the
+ * first entry in cc_callwheel that may need handling. In turn,
+ * a softclock() is scheduled so it can serve the various entries i
+ * such that cc_softclock <= i <= cc_ticks .
+ * XXX maybe cc_softclock and cc_ticks should be volatile ?
+ *
+ * cc_ticks is also used in callout_reset_cpu() to determine
+ * when the callout should be served.
+ */
struct callout_cpu {
struct mtx cc_lock;
struct callout *cc_callout;
@@ -90,6 +107,7 @@ struct callout_cpu {
struct callout *cc_next;
struct callout *cc_curr;
void *cc_cookie;
+ int cc_ticks;
int cc_softticks;
int cc_cancel;
int cc_waiting;
@@ -244,7 +262,8 @@ callout_tick(void)
need_softclock = 0;
cc = CC_SELF();
mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
- for (; (cc->cc_softticks - ticks) < 0; cc->cc_softticks++) {
+ cc->cc_ticks++;
+ for (; (cc->cc_softticks - cc->cc_ticks) <= 0; cc->cc_softticks++) {
bucket = cc->cc_softticks & callwheelmask;
if (!TAILQ_EMPTY(&cc->cc_callwheel[bucket])) {
need_softclock = 1;
@@ -323,7 +342,7 @@ softclock(void *arg)
steps = 0;
cc = (struct callout_cpu *)arg;
CC_LOCK(cc);
- while (cc->cc_softticks != ticks) {
+ while (cc->cc_softticks - 1 != cc->cc_ticks) {
/*
* cc_softticks may be modified by hard clock, so cache
* it while we work on a given bucket.
@@ -622,7 +641,7 @@ retry:
c->c_arg = arg;
c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
c->c_func = ftn;
- c->c_time = ticks + to_ticks;
+ c->c_time = cc->cc_ticks + to_ticks;
TAILQ_INSERT_TAIL(&cc->cc_callwheel[c->c_time & callwheelmask],
c, c_links.tqe);
CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
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