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MFC r197137 and r200510, which fixes a problem in 8.0

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with callouts firing one tick too late. See the logs for
the original patch for details.
RELENG_7 is not affected by the problem.
This commit is contained in:
Luigi Rizzo 2010-03-07 14:29:12 +00:00
parent 90cb9e50f4
commit f078d8617f
1 changed files with 22 additions and 3 deletions
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25
sys/kern/kern_timeout.c
View file

@ -82,6 +82,23 @@ SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
*/
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",