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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