Date: Sun, 7 Mar 2010 14:29:12 +0000 (UTC) From: Luigi Rizzo <luigi@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org Subject: svn commit: r204831 - stable/8/sys/kern Message-ID: <201003071429.o27ETCmL073637@svn.freebsd.org>
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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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