- Make SCHED_STATS more generic by adding a wrapper to create the

   variables and sysctl nodes.
 - In reset walk the children of kern_sched_stats and reset the counters
   via the oid_arg1 pointer.  This allows us to add arbitrary counters to
   the tree and still reset them properly.
 - Define a set of switch types to be passed with flags to mi_switch().
   These types are named SWT_*.  These types correspond to SCHED_STATS
   counters and are automatically handled in this way.
 - Make the new SWT_ types more specific than the older switch stats.
   There are now stats for idle switches, remote idle wakeups, remote
   preemption ithreads idling, etc.
 - Add switch statistics for ULE's pickcpu algorithm.  These stats include
   how much migration there is, how often affinity was successful, how
   often threads were migrated to the local cpu on wakeup, etc.

Sponsored by:	Nokia

15 files changed, 122 insertions, 67 deletions

diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
index e626988..5e464f9 100644
--- a/sys/kern/kern_intr.c
+++ b/sys/kern/kern_intr.c
@@ -1231,7 +1231,7 @@ ithread_loop(void *arg)
 		if (!ithd->it_need && !(ithd->it_flags & IT_DEAD)) {
 			TD_SET_IWAIT(td);
 			ie->ie_count = 0;
-			mi_switch(SW_VOL, NULL);
+			mi_switch(SW_VOL | SWT_IWAIT, NULL);
 		}
 		thread_unlock(td);
 	}
@@ -1389,7 +1389,7 @@ ithread_loop(void *arg)
 		if (!ithd->it_need && !(ithd->it_flags & IT_DEAD)) {
 			TD_SET_IWAIT(td);
 			ie->ie_count = 0;
-			mi_switch(SW_VOL, NULL);
+			mi_switch(SW_VOL | SWT_IWAIT, NULL);
 		}
 		thread_unlock(td);
 	}
diff --git a/sys/kern/kern_subr.c b/sys/kern/kern_subr.c
index 2101026..c93f262 100644
--- a/sys/kern/kern_subr.c
+++ b/sys/kern/kern_subr.c
@@ -456,7 +456,7 @@ uio_yield(void)
 	DROP_GIANT();
 	thread_lock(td);
 	sched_prio(td, td->td_user_pri);
-	mi_switch(SW_INVOL, NULL);
+	mi_switch(SW_INVOL | SWT_RELINQUISH, NULL);
 	thread_unlock(td);
 	PICKUP_GIANT();
 }
diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c
index 10bfb73..b7cb0b6 100644
--- a/sys/kern/kern_switch.c
+++ b/sys/kern/kern_switch.c
@@ -73,25 +73,35 @@ static int kern_sched_preemption = 0;
 SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD,
     &kern_sched_preemption, 0, "Kernel preemption enabled");
 
+/*
+ * Support for scheduler stats exported via kern.sched.stats.  All stats may
+ * be reset with kern.sched.stats.reset = 1.  Stats may be defined elsewhere
+ * with SCHED_STAT_DEFINE().
+ */
 #ifdef SCHED_STATS
-long switch_preempt;
-long switch_owepreempt;
-long switch_turnstile;
-long switch_sleepq;
-long switch_sleepqtimo;
-long switch_relinquish;
-long switch_needresched;
-static SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, preempt, CTLFLAG_RD, &switch_preempt, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, owepreempt, CTLFLAG_RD, &switch_owepreempt, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, turnstile, CTLFLAG_RD, &switch_turnstile, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, sleepq, CTLFLAG_RD, &switch_sleepq, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, sleepqtimo, CTLFLAG_RD, &switch_sleepqtimo, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, relinquish, CTLFLAG_RD, &switch_relinquish, 0, "");
-SYSCTL_INT(_kern_sched_stats, OID_AUTO, needresched, CTLFLAG_RD, &switch_needresched, 0, "");
+long sched_switch_stats[SWT_COUNT];	/* Switch reasons from mi_switch(). */
+
+SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats");
+SCHED_STAT_DEFINE_VAR(uncategorized, &sched_switch_stats[SWT_NONE], "");
+SCHED_STAT_DEFINE_VAR(preempt, &sched_switch_stats[SWT_PREEMPT], "");
+SCHED_STAT_DEFINE_VAR(owepreempt, &sched_switch_stats[SWT_OWEPREEMPT], "");
+SCHED_STAT_DEFINE_VAR(turnstile, &sched_switch_stats[SWT_TURNSTILE], "");
+SCHED_STAT_DEFINE_VAR(sleepq, &sched_switch_stats[SWT_SLEEPQ], "");
+SCHED_STAT_DEFINE_VAR(sleepqtimo, &sched_switch_stats[SWT_SLEEPQTIMO], "");
+SCHED_STAT_DEFINE_VAR(relinquish, &sched_switch_stats[SWT_RELINQUISH], "");
+SCHED_STAT_DEFINE_VAR(needresched, &sched_switch_stats[SWT_NEEDRESCHED], "");
+SCHED_STAT_DEFINE_VAR(idle, &sched_switch_stats[SWT_IDLE], "");
+SCHED_STAT_DEFINE_VAR(iwait, &sched_switch_stats[SWT_IWAIT], "");
+SCHED_STAT_DEFINE_VAR(suspend, &sched_switch_stats[SWT_SUSPEND], "");
+SCHED_STAT_DEFINE_VAR(remotepreempt, &sched_switch_stats[SWT_REMOTEPREEMPT],
+    "");
+SCHED_STAT_DEFINE_VAR(remotewakeidle, &sched_switch_stats[SWT_REMOTEWAKEIDLE],
+    "");
+
 static int
 sysctl_stats_reset(SYSCTL_HANDLER_ARGS)
 {
+	struct sysctl_oid *p;
         int error;
 	int val;
 
@@ -101,14 +111,15 @@ sysctl_stats_reset(SYSCTL_HANDLER_ARGS)
                 return (error);
         if (val == 0)
                 return (0);
-	switch_preempt = 0;
-	switch_owepreempt = 0;
-	switch_turnstile = 0;
-	switch_sleepq = 0;
-	switch_sleepqtimo = 0;
-	switch_relinquish = 0;
-	switch_needresched = 0;
-
+	/*
+	 * Traverse the list of children of _kern_sched_stats and reset each
+	 * to 0.  Skip the reset entry.
+	 */
+	SLIST_FOREACH(p, oidp->oid_parent, oid_link) {
+		if (p == oidp || p->oid_arg1 == NULL)
+			continue;
+		*(long *)p->oid_arg1 = 0;
+	}
 	return (0);
 }
 
@@ -164,6 +175,7 @@ void
 critical_exit(void)
 {
 	struct thread *td;
+	int flags;
 
 	td = curthread;
 	KASSERT(td->td_critnest != 0,
@@ -175,8 +187,12 @@ critical_exit(void)
 			td->td_critnest = 1;
 			thread_lock(td);
 			td->td_critnest--;
-			SCHED_STAT_INC(switch_owepreempt);
-			mi_switch(SW_INVOL|SW_PREEMPT, NULL);
+			flags = SW_INVOL | SW_PREEMPT;
+			if (TD_IS_IDLETHREAD(td))
+				flags |= SWT_IDLE;
+			else
+				flags |= SWT_OWEPREEMPT;
+			mi_switch(flags, NULL);
 			thread_unlock(td);
 		}
 	} else
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index b4defe9..c322ace 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -38,6 +38,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_ktrace.h"
+#include "opt_sched.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -390,6 +391,9 @@ mi_switch(int flags, struct thread *newtd)
 		td->td_ru.ru_nvcsw++;
 	else
 		td->td_ru.ru_nivcsw++;
+#ifdef SCHED_STATS
+	SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
+#endif
 	/*
 	 * Compute the amount of time during which the current
 	 * thread was running, and add that to its total so far.
@@ -533,7 +537,7 @@ yield(struct thread *td, struct yield_args *uap)
 
 	thread_lock(td);
 	sched_prio(td, PRI_MAX_TIMESHARE);
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
 	thread_unlock(td);
 	td->td_retval[0] = 0;
 	return (0);
diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
index 8745e5e..a3d5da7 100644
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -723,7 +723,7 @@ thread_suspend_check(int return_instead)
 			td->td_flags |= TDF_BOUNDARY;
 		}
 		PROC_SUNLOCK(p);
-		mi_switch(SW_INVOL, NULL);
+		mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
 		if (return_instead == 0)
 			td->td_flags &= ~TDF_BOUNDARY;
 		thread_unlock(td);
@@ -756,7 +756,7 @@ thread_suspend_switch(struct thread *td)
 	sched_sleep(td, 0);
 	PROC_SUNLOCK(p);
 	DROP_GIANT();
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_SUSPEND, NULL);
 	thread_unlock(td);
 	PICKUP_GIANT();
 	PROC_LOCK(p);
diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
index 6879801..ed5cf62 100644
--- a/sys/kern/sched_4bsd.c
+++ b/sys/kern/sched_4bsd.c
@@ -316,8 +316,7 @@ maybe_preempt(struct thread *td)
 	TD_SET_RUNNING(td);
 	CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td,
 	    td->td_proc->p_pid, td->td_name);
-	SCHED_STAT_INC(switch_preempt);
-	mi_switch(SW_INVOL|SW_PREEMPT, td);
+	mi_switch(SW_INVOL | SW_PREEMPT | SWT_PREEMPT, td);
 	/*
 	 * td's lock pointer may have changed.  We have to return with it
 	 * locked.
@@ -1332,7 +1331,7 @@ sched_preempt(struct thread *td)
 	if (td->td_critnest > 1)
 		td->td_owepreempt = 1;
 	else
-		mi_switch(SW_INVOL | SW_PREEMPT, NULL);
+		mi_switch(SW_INVOL | SW_PREEMPT | SWT_PREEMPT, NULL);
 	thread_unlock(td);
 }
 
@@ -1397,8 +1396,7 @@ void
 sched_relinquish(struct thread *td)
 {
 	thread_lock(td);
-	SCHED_STAT_INC(switch_relinquish);
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
 	thread_unlock(td);
 }
 
@@ -1448,7 +1446,7 @@ sched_idletd(void *dummy)
 			cpu_idle();
 
 		mtx_lock_spin(&sched_lock);
-		mi_switch(SW_VOL, NULL);
+		mi_switch(SW_VOL | SWT_IDLE, NULL);
 		mtx_unlock_spin(&sched_lock);
 	}
 }
diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 911b169..c03f7c8 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -909,7 +909,7 @@ tdq_idled(struct tdq *tdq)
 		}
 		spinlock_exit();
 		TDQ_UNLOCK(steal);
-		mi_switch(SW_VOL, NULL);
+		mi_switch(SW_VOL | SWT_IDLE, NULL);
 		thread_unlock(curthread);
 
 		return (0);
@@ -1073,6 +1073,13 @@ sched_setcpu(struct thread *td, int cpu, int flags)
 	return (tdq);
 }
 
+SCHED_STAT_DEFINE(pickcpu_intrbind, "Soft interrupt binding");
+SCHED_STAT_DEFINE(pickcpu_idle_affinity, "Picked idle cpu based on affinity");
+SCHED_STAT_DEFINE(pickcpu_affinity, "Picked cpu based on affinity");
+SCHED_STAT_DEFINE(pickcpu_lowest, "Selected lowest load");
+SCHED_STAT_DEFINE(pickcpu_local, "Migrated to current cpu");
+SCHED_STAT_DEFINE(pickcpu_migration, "Selection may have caused migration");
+
 static int
 sched_pickcpu(struct thread *td, int flags)
 {
@@ -1098,8 +1105,10 @@ sched_pickcpu(struct thread *td, int flags)
 	 * the interrupt.
 	 */
 	if (td->td_priority <= PRI_MAX_ITHD && THREAD_CAN_SCHED(td, self) &&
-	    curthread->td_intr_nesting_level)
+	    curthread->td_intr_nesting_level && ts->ts_cpu != self) {
+		SCHED_STAT_INC(pickcpu_intrbind);
 		ts->ts_cpu = self;
+	}
 	/*
 	 * If the thread can run on the last cpu and the affinity has not
 	 * expired or it is idle run it there.
@@ -1107,10 +1116,14 @@ sched_pickcpu(struct thread *td, int flags)
 	pri = td->td_priority;
 	tdq = TDQ_CPU(ts->ts_cpu);
 	if (THREAD_CAN_SCHED(td, ts->ts_cpu)) {
-		if (tdq->tdq_lowpri > PRI_MIN_IDLE)
+		if (tdq->tdq_lowpri > PRI_MIN_IDLE) {
+			SCHED_STAT_INC(pickcpu_idle_affinity);
 			return (ts->ts_cpu);
-		if (SCHED_AFFINITY(ts, CG_SHARE_L2) && tdq->tdq_lowpri > pri)
+		}
+		if (SCHED_AFFINITY(ts, CG_SHARE_L2) && tdq->tdq_lowpri > pri) {
+			SCHED_STAT_INC(pickcpu_affinity);
 			return (ts->ts_cpu);
+		}
 	}
 	/*
 	 * Search for the highest level in the tree that still has affinity.
@@ -1129,8 +1142,13 @@ sched_pickcpu(struct thread *td, int flags)
 	 * Compare the lowest loaded cpu to current cpu.
 	 */
 	if (THREAD_CAN_SCHED(td, self) && TDQ_CPU(self)->tdq_lowpri > pri &&
-	    TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE)
+	    TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE) {
+		SCHED_STAT_INC(pickcpu_local);
 		cpu = self;
+	} else
+		SCHED_STAT_INC(pickcpu_lowest);
+	if (cpu != ts->ts_cpu)
+		SCHED_STAT_INC(pickcpu_migration);
 	KASSERT(cpu != -1, ("sched_pickcpu: Failed to find a cpu."));
 	return (cpu);
 }
@@ -1989,10 +2007,15 @@ sched_preempt(struct thread *td)
 	TDQ_LOCK_ASSERT(tdq, MA_OWNED);
 	tdq->tdq_ipipending = 0;
 	if (td->td_priority > tdq->tdq_lowpri) {
+		int flags;
+
+		flags = SW_INVOL | SW_PREEMPT;
 		if (td->td_critnest > 1)
 			td->td_owepreempt = 1;
+		else if (TD_IS_IDLETHREAD(td))
+			mi_switch(flags | SWT_REMOTEWAKEIDLE, NULL);
 		else
-			mi_switch(SW_INVOL | SW_PREEMPT, NULL);
+			mi_switch(flags | SWT_REMOTEPREEMPT, NULL);
 	}
 	thread_unlock(td);
 }
@@ -2378,8 +2401,7 @@ void
 sched_relinquish(struct thread *td)
 {
 	thread_lock(td);
-	SCHED_STAT_INC(switch_relinquish);
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
 	thread_unlock(td);
 }
 
diff --git a/sys/kern/subr_sleepqueue.c b/sys/kern/subr_sleepqueue.c
index 9edd56e..1dbd1db 100644
--- a/sys/kern/subr_sleepqueue.c
+++ b/sys/kern/subr_sleepqueue.c
@@ -486,8 +486,7 @@ sleepq_switch(void *wchan, int pri)
 	sched_sleep(td, pri);
 	thread_lock_set(td, &sc->sc_lock);
 	TD_SET_SLEEPING(td);
-	SCHED_STAT_INC(switch_sleepq);
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_SLEEPQ, NULL);
 	KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
 	CTR3(KTR_PROC, "sleepq resume: thread %p (pid %ld, %s)",
 	    (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
@@ -527,8 +526,7 @@ sleepq_check_timeout(void)
 	else if (callout_stop(&td->td_slpcallout) == 0) {
 		td->td_flags |= TDF_TIMEOUT;
 		TD_SET_SLEEPING(td);
-		SCHED_STAT_INC(switch_sleepqtimo);
-		mi_switch(SW_INVOL, NULL);
+		mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL);
 	}
 	return (0);
 }
diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
index a92abd2..3d1948d 100644
--- a/sys/kern/subr_trap.c
+++ b/sys/kern/subr_trap.c
@@ -211,8 +211,7 @@ ast(struct trapframe *framep)
 #endif
 		thread_lock(td);
 		sched_prio(td, td->td_user_pri);
-		SCHED_STAT_INC(switch_needresched);
-		mi_switch(SW_INVOL, NULL);
+		mi_switch(SW_INVOL | SWT_NEEDRESCHED, NULL);
 		thread_unlock(td);
 #ifdef KTRACE
 		if (KTRPOINT(td, KTR_CSW))
diff --git a/sys/kern/subr_turnstile.c b/sys/kern/subr_turnstile.c
index fd6cdbd..7b8270a 100644
--- a/sys/kern/subr_turnstile.c
+++ b/sys/kern/subr_turnstile.c
@@ -741,8 +741,7 @@ turnstile_wait(struct turnstile *ts, struct thread *owner, int queue)
 		    td->td_tid, lock, lock->lo_name);
 
 	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
-	SCHED_STAT_INC(switch_turnstile);
-	mi_switch(SW_VOL, NULL);
+	mi_switch(SW_VOL | SWT_TURNSTILE, NULL);
 
 	if (LOCK_LOG_TEST(lock, 0))
 		CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index a3e055f..86adbb1 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -588,10 +588,26 @@ struct proc {
 
 #ifdef _KERNEL
 
-/* Flags for mi_switch(). */
-#define	SW_VOL		0x0001		/* Voluntary switch. */
-#define	SW_INVOL	0x0002		/* Involuntary switch. */
-#define SW_PREEMPT	0x0004		/* The invol switch is a preemption */
+/* Types and flags for mi_switch(). */
+#define	SW_TYPE_MASK		0xff	/* First 8 bits are switch type */
+#define	SWT_NONE		0	/* Unspecified switch. */
+#define	SWT_PREEMPT		1	/* Switching due to preemption. */
+#define	SWT_OWEPREEMPT		2	/* Switching due to opepreempt. */
+#define	SWT_TURNSTILE		3	/* Turnstile contention. */
+#define	SWT_SLEEPQ		4	/* Sleepq wait. */
+#define	SWT_SLEEPQTIMO		5	/* Sleepq timeout wait. */
+#define	SWT_RELINQUISH		6	/* yield call. */
+#define	SWT_NEEDRESCHED		7	/* NEEDRESCHED was set. */
+#define	SWT_IDLE		8	/* Switching from the idle thread. */
+#define	SWT_IWAIT		9	/* Waiting for interrupts. */
+#define	SWT_SUSPEND		10	/* Thread suspended. */
+#define	SWT_REMOTEPREEMPT	11	/* Remote processor preempted. */
+#define	SWT_REMOTEWAKEIDLE	12	/* Remote processor preempted idle. */
+#define	SWT_COUNT		13	/* Number of switch types. */
+/* Flags */
+#define	SW_VOL		0x0100		/* Voluntary switch. */
+#define	SW_INVOL	0x0200		/* Involuntary switch. */
+#define SW_PREEMPT	0x0400		/* The invol switch is a preemption */
 
 /* How values for thread_single(). */
 #define	SINGLE_NO_EXIT	0
diff --git a/sys/sys/sched.h b/sys/sys/sched.h
index fa57055..bbd2199 100644
--- a/sys/sys/sched.h
+++ b/sys/sys/sched.h
@@ -154,17 +154,19 @@ sched_unpin(void)
 #define	SRQ_PREEMPTED	0x0008		/* has been preempted.. be kind */
 #define	SRQ_BORROWING	0x0010		/* Priority updated due to prio_lend */
 
-/* Switch stats. */
+/* Scheduler stats. */
 #ifdef SCHED_STATS
-extern long switch_preempt;
-extern long switch_owepreempt;
-extern long switch_turnstile;
-extern long switch_sleepq;
-extern long switch_sleepqtimo;
-extern long switch_relinquish;
-extern long switch_needresched;
+extern long sched_switch_stats[SWT_COUNT];
+
+#define	SCHED_STAT_DEFINE_VAR(name, ptr, descr)				\
+    SYSCTL_LONG(_kern_sched_stats, OID_AUTO, name, CTLFLAG_RD, ptr, 0, descr)
+#define	SCHED_STAT_DEFINE(name, descr)					\
+    unsigned long name;							\
+    SCHED_STAT_DEFINE_VAR(name, &name, descr)
 #define SCHED_STAT_INC(var)     atomic_add_long(&(var), 1)
 #else
+#define	SCHED_STAT_DEFINE_VAR(name, descr, ptr)
+#define	SCHED_STAT_DEFINE(name, descr)
 #define SCHED_STAT_INC(var)
 #endif
 
diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index 59543ba..ebd83e7 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -632,6 +632,7 @@ SYSCTL_DECL(_kern_features);
 SYSCTL_DECL(_kern_ipc);
 SYSCTL_DECL(_kern_proc);
 SYSCTL_DECL(_kern_sched);
+SYSCTL_DECL(_kern_sched_stats);
 SYSCTL_DECL(_sysctl);
 SYSCTL_DECL(_vm);
 SYSCTL_DECL(_vm_stats);
diff --git a/sys/vm/vm_glue.c b/sys/vm/vm_glue.c
index 9f9dc5a..462c460 100644
--- a/sys/vm/vm_glue.c
+++ b/sys/vm/vm_glue.c
@@ -735,7 +735,7 @@ loop:
 		thread_lock(&thread0);
 		if (!proc0_rescan) {
 			TD_SET_IWAIT(&thread0);
-			mi_switch(SW_VOL, NULL);
+			mi_switch(SW_VOL | SWT_IWAIT, NULL);
 		}
 		proc0_rescan = 0;
 		thread_unlock(&thread0);
diff --git a/sys/vm/vm_zeroidle.c b/sys/vm/vm_zeroidle.c
index c82de5a..9e1970a 100644
--- a/sys/vm/vm_zeroidle.c
+++ b/sys/vm/vm_zeroidle.c
@@ -127,7 +127,7 @@ vm_pagezero(void __unused *arg)
 #ifndef PREEMPTION
 			if (sched_runnable()) {
 				thread_lock(curthread);
-				mi_switch(SW_VOL, NULL);
+				mi_switch(SW_VOL | SWT_IDLE, NULL);
 				thread_unlock(curthread);
 			}
 #endif