John Baldwin wrote: > On Sunday 15 June 2008 07:23:19 am Stef Walter wrote: >> I've been trying to track down a deadlock on some newish production >> servers running FreeBSD 6.3-RELEASE-p2. The deadlock occurs on a >> specific (although mundane) hardware configuration, and each of several >> servers running this hardware deadlock about once per week. > > Try this change: > <snip> > We use it at work on 6.x. W/o this fix, round-robin stops working on 4BSD > when softclock() (swi4: clock) blocks on a lock like Giant.
Just wanted to confirm: That patch did the trick. All the SMP machines that had this problem have been stable for 11 days now, longer than any of them were up previously. I changed the patch slightly to work with FreeBSD 6.3-RELEASE. That's attached, in case anyone needs this later. Cheers, Stef
--- sys/kern/sched_4bsd.c.orig 2006-06-16 22:11:55.000000000 +0000 +++ sys/kern/sched_4bsd.c 2008-06-18 17:04:34.000000000 +0000 @@ -157,13 +157,10 @@ static int sched_quantum; /* Roundrobin scheduling quantum in ticks. */ #define SCHED_QUANTUM (hz / 10) /* Default sched quantum */ -static struct callout roundrobin_callout; - static void slot_fill(struct ksegrp *kg); static struct kse *sched_choose(void); /* XXX Should be thread * */ static void setup_runqs(void); -static void roundrobin(void *arg); static void schedcpu(void); static void schedcpu_thread(void); static void sched_priority(struct thread *td, u_char prio); @@ -316,27 +313,6 @@ } /* - * Force switch among equal priority processes every 100ms. - * We don't actually need to force a context switch of the current process. - * The act of firing the event triggers a context switch to softclock() and - * then switching back out again which is equivalent to a preemption, thus - * no further work is needed on the local CPU. - */ -/* ARGSUSED */ -static void -roundrobin(void *arg) -{ - -#ifdef SMP - mtx_lock_spin(&sched_lock); - forward_roundrobin(); - mtx_unlock_spin(&sched_lock); -#endif - - callout_reset(&roundrobin_callout, sched_quantum, roundrobin, NULL); -} - -/* * Constants for digital decay and forget: * 90% of (kg_estcpu) usage in 5 * loadav time * 95% of (ke_pctcpu) usage in 60 seconds (load insensitive) @@ -618,11 +594,6 @@ sched_quantum = SCHED_QUANTUM; hogticks = 2 * sched_quantum; - callout_init(&roundrobin_callout, CALLOUT_MPSAFE); - - /* Kick off timeout driven events by calling first time. */ - roundrobin(NULL); - /* Account for thread0. */ sched_load_add(); } @@ -697,6 +668,14 @@ resetpriority(kg); resetpriority_thread(td, kg); } + + /* + * Force a context switch if the current thread has used up a full + * quantum (default quantum is 100ms). + */ + if (!((td)->td_flags & TDF_IDLETD) && + ticks - PCPU_GET(switchticks) >= sched_quantum) + td->td_flags |= TDF_NEEDRESCHED; } /*
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