- Create a new scheduler api that is defined in sys/sched.h

 - Begin moving scheduler specific functionality into sched_4bsd.c
 - Replace direct manipulation of scheduler data with hooks provided by the
   new api.
 - Remove KSE specific state modifications and single runq assumptions from
   kern_switch.c

Reviewed by:	-arch

1 files changed, 635 insertions, 0 deletions

diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
new file mode 100644
index 0000000..99d23aa
--- /dev/null
+++ b/sys/kern/sched_4bsd.c
@@ -0,0 +1,635 @@
+/*-
+ * Copyright (c) 1982, 1986, 1990, 1991, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ * (c) UNIX System Laboratories, Inc.
+ * All or some portions of this file are derived from material licensed
+ * to the University of California by American Telephone and Telegraph
+ * Co. or Unix System Laboratories, Inc. and are reproduced herein with
+ * the permission of UNIX System Laboratories, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the University of
+ *	California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/kernel.h>
+#include <sys/ktr.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/proc.h>
+#include <sys/resourcevar.h>
+#include <sys/sched.h>
+#include <sys/smp.h>
+#include <sys/sysctl.h>
+#include <sys/sx.h>
+
+
+static int	sched_quantum;	/* Roundrobin scheduling quantum in ticks. */
+#define	SCHED_QUANTUM	(hz / 10);	/* Default sched quantum */
+
+static struct callout schedcpu_callout;
+static struct callout roundrobin_callout;
+
+static void	roundrobin(void *arg);
+static void	schedcpu(void *arg);
+static void	sched_setup(void *dummy);
+static void	maybe_resched(struct thread *td);
+static void	updatepri(struct ksegrp *kg);
+static void	resetpriority(struct ksegrp *kg);
+
+SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)
+
+/*
+ * Global run queue.
+ */
+static struct runq runq;
+SYSINIT(runq, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, runq_init, &runq)
+
+static int
+sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
+{
+	int error, new_val;
+
+	new_val = sched_quantum * tick;
+	error = sysctl_handle_int(oidp, &new_val, 0, req);
+        if (error != 0 || req->newptr == NULL)
+		return (error);
+	if (new_val < tick)
+		return (EINVAL);
+	sched_quantum = new_val / tick;
+	hogticks = 2 * sched_quantum;
+	return (0);
+}
+
+SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
+	0, sizeof sched_quantum, sysctl_kern_quantum, "I",
+	"Roundrobin scheduling quantum in microseconds");
+
+/*
+ * Arrange to reschedule if necessary, taking the priorities and
+ * schedulers into account.
+ */
+static void
+maybe_resched(struct thread *td)
+{
+
+	mtx_assert(&sched_lock, MA_OWNED);
+	if (td->td_priority < curthread->td_priority)
+		curthread->td_kse->ke_flags |= KEF_NEEDRESCHED;
+}
+
+/*
+ * 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 (p_estcpu) usage in 5 * loadav time
+ *	95% of (p_pctcpu) usage in 60 seconds (load insensitive)
+ *          Note that, as ps(1) mentions, this can let percentages
+ *          total over 100% (I've seen 137.9% for 3 processes).
+ *
+ * Note that schedclock() updates p_estcpu and p_cpticks asynchronously.
+ *
+ * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
+ * That is, the system wants to compute a value of decay such
+ * that the following for loop:
+ * 	for (i = 0; i < (5 * loadavg); i++)
+ * 		p_estcpu *= decay;
+ * will compute
+ * 	p_estcpu *= 0.1;
+ * for all values of loadavg:
+ *
+ * Mathematically this loop can be expressed by saying:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * The system computes decay as:
+ * 	decay = (2 * loadavg) / (2 * loadavg + 1)
+ *
+ * We wish to prove that the system's computation of decay
+ * will always fulfill the equation:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * If we compute b as:
+ * 	b = 2 * loadavg
+ * then
+ * 	decay = b / (b + 1)
+ *
+ * We now need to prove two things:
+ *	1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
+ *	2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
+ *
+ * Facts:
+ *         For x close to zero, exp(x) =~ 1 + x, since
+ *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
+ *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
+ *         For x close to zero, ln(1+x) =~ x, since
+ *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
+ *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
+ *         ln(.1) =~ -2.30
+ *
+ * Proof of (1):
+ *    Solve (factor)**(power) =~ .1 given power (5*loadav):
+ *	solving for factor,
+ *      ln(factor) =~ (-2.30/5*loadav), or
+ *      factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
+ *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
+ *
+ * Proof of (2):
+ *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
+ *	solving for power,
+ *      power*ln(b/(b+1)) =~ -2.30, or
+ *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
+ *
+ * Actual power values for the implemented algorithm are as follows:
+ *      loadav: 1       2       3       4
+ *      power:  5.68    10.32   14.94   19.55
+ */
+
+/* calculations for digital decay to forget 90% of usage in 5*loadav sec */
+#define	loadfactor(loadav)	(2 * (loadav))
+#define	decay_cpu(loadfac, cpu)	(((loadfac) * (cpu)) / ((loadfac) + FSCALE))
+
+/* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
+static fixpt_t	ccpu = 0.95122942450071400909 * FSCALE;	/* exp(-1/20) */
+SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
+
+/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
+static int	fscale __unused = FSCALE;
+SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
+
+/*
+ * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
+ * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
+ * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
+ *
+ * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
+ *	1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
+ *
+ * If you don't want to bother with the faster/more-accurate formula, you
+ * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
+ * (more general) method of calculating the %age of CPU used by a process.
+ */
+#define	CCPU_SHIFT	11
+
+/*
+ * Recompute process priorities, every hz ticks.
+ * MP-safe, called without the Giant mutex.
+ */
+/* ARGSUSED */
+static void
+schedcpu(void *arg)
+{
+	register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
+	struct thread *td;
+	struct proc *p;
+	struct kse *ke;
+	struct ksegrp *kg;
+	int realstathz;
+	int awake;
+
+	realstathz = stathz ? stathz : hz;
+	sx_slock(&allproc_lock);
+	FOREACH_PROC_IN_SYSTEM(p) {
+		mtx_lock_spin(&sched_lock);
+		p->p_swtime++;
+		FOREACH_KSEGRP_IN_PROC(p, kg) { 
+			awake = 0;
+			FOREACH_KSE_IN_GROUP(kg, ke) {
+				/*
+				 * Increment time in/out of memory and sleep
+				 * time (if sleeping).  We ignore overflow;
+				 * with 16-bit int's (remember them?)
+				 * overflow takes 45 days.
+				 */
+				/*
+				 * The kse slptimes are not touched in wakeup
+				 * because the thread may not HAVE a KSE.
+				 */
+				if (ke->ke_state == KES_ONRUNQ) {
+					awake = 1;
+					ke->ke_flags &= ~KEF_DIDRUN;
+				} else if ((ke->ke_state == KES_THREAD) &&
+				    (TD_IS_RUNNING(ke->ke_thread))) {
+					awake = 1;
+					/* Do not clear KEF_DIDRUN */
+				} else if (ke->ke_flags & KEF_DIDRUN) {
+					awake = 1;
+					ke->ke_flags &= ~KEF_DIDRUN;
+				}
+
+				/*
+				 * pctcpu is only for ps?
+				 * Do it per kse.. and add them up at the end?
+				 * XXXKSE
+				 */
+				ke->ke_pctcpu
+				    = (ke->ke_pctcpu * ccpu) >> FSHIFT;
+				/*
+				 * If the kse has been idle the entire second,
+				 * stop recalculating its priority until
+				 * it wakes up.
+				 */
+				if (ke->ke_cpticks == 0)
+					continue;
+#if	(FSHIFT >= CCPU_SHIFT)
+				ke->ke_pctcpu += (realstathz == 100) ?
+				    ((fixpt_t) ke->ke_cpticks) <<
+				    (FSHIFT - CCPU_SHIFT) :
+				    100 * (((fixpt_t) ke->ke_cpticks) <<
+				    (FSHIFT - CCPU_SHIFT)) / realstathz;
+#else
+				ke->ke_pctcpu += ((FSCALE - ccpu) *
+				    (ke->ke_cpticks * FSCALE / realstathz)) >>
+				    FSHIFT;
+#endif
+				ke->ke_cpticks = 0;
+			} /* end of kse loop */
+			/* 
+			 * If there are ANY running threads in this KSEGRP,
+			 * then don't count it as sleeping.
+			 */
+			if (awake) {
+				if (kg->kg_slptime > 1) {
+					/*
+					 * In an ideal world, this should not
+					 * happen, because whoever woke us
+					 * up from the long sleep should have
+					 * unwound the slptime and reset our
+					 * priority before we run at the stale
+					 * priority.  Should KASSERT at some
+					 * point when all the cases are fixed.
+					 */
+					updatepri(kg);
+				}
+				kg->kg_slptime = 0;
+			} else {
+				kg->kg_slptime++;
+			}
+			if (kg->kg_slptime > 1)
+				continue;
+			kg->kg_estcpu = decay_cpu(loadfac, kg->kg_estcpu);
+		      	resetpriority(kg);
+			FOREACH_THREAD_IN_GROUP(kg, td) {
+				int changedqueue;
+				if (td->td_priority >= PUSER) {
+					/*
+					 * Only change the priority
+					 * of threads that are still at their
+					 * user priority. 
+					 * XXXKSE This is problematic
+					 * as we may need to re-order
+					 * the threads on the KSEG list.
+					 */
+					changedqueue =
+					    ((td->td_priority / RQ_PPQ) !=
+					     (kg->kg_user_pri / RQ_PPQ));
+
+					td->td_priority = kg->kg_user_pri;
+					if (changedqueue && TD_ON_RUNQ(td)) {
+						/* this could be optimised */
+						remrunqueue(td);
+						td->td_priority =
+						    kg->kg_user_pri;
+						setrunqueue(td);
+					} else {
+						td->td_priority = kg->kg_user_pri;
+					}
+				}
+			}
+		} /* end of ksegrp loop */
+		mtx_unlock_spin(&sched_lock);
+	} /* end of process loop */
+	sx_sunlock(&allproc_lock);
+	wakeup(&lbolt);
+	callout_reset(&schedcpu_callout, hz, schedcpu, NULL);
+}
+
+/*
+ * Recalculate the priority of a process after it has slept for a while.
+ * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
+ * least six times the loadfactor will decay p_estcpu to zero.
+ */
+static void
+updatepri(struct ksegrp *kg)
+{
+	register unsigned int newcpu;
+	register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
+
+	newcpu = kg->kg_estcpu;
+	if (kg->kg_slptime > 5 * loadfac)
+		kg->kg_estcpu = 0;
+	else {
+		kg->kg_slptime--;	/* the first time was done in schedcpu */
+		while (newcpu && --kg->kg_slptime)
+			newcpu = decay_cpu(loadfac, newcpu);
+		kg->kg_estcpu = newcpu;
+	}
+	resetpriority(kg);
+}
+
+/*
+ * Compute the priority of a process when running in user mode.
+ * Arrange to reschedule if the resulting priority is better
+ * than that of the current process.
+ */
+static void
+resetpriority(struct ksegrp *kg)
+{
+	register unsigned int newpriority;
+	struct thread *td;
+
+	mtx_lock_spin(&sched_lock);
+	if (kg->kg_pri_class == PRI_TIMESHARE) {
+		newpriority = PUSER + kg->kg_estcpu / INVERSE_ESTCPU_WEIGHT +
+		    NICE_WEIGHT * (kg->kg_nice - PRIO_MIN);
+		newpriority = min(max(newpriority, PRI_MIN_TIMESHARE),
+		    PRI_MAX_TIMESHARE);
+		kg->kg_user_pri = newpriority;
+	}
+	FOREACH_THREAD_IN_GROUP(kg, td) {
+		maybe_resched(td);			/* XXXKSE silly */
+	}
+	mtx_unlock_spin(&sched_lock);
+}
+
+/* ARGSUSED */
+static void
+sched_setup(void *dummy)
+{
+	if (sched_quantum == 0)
+		sched_quantum = SCHED_QUANTUM;
+	hogticks = 2 * sched_quantum;
+
+	callout_init(&schedcpu_callout, 1);
+	callout_init(&roundrobin_callout, 0);
+
+	/* Kick off timeout driven events by calling first time. */
+	roundrobin(NULL);
+	schedcpu(NULL);
+}
+
+/* External interfaces start here */
+int
+sched_runnable(void)
+{
+        return runq_check(&runq);
+}
+
+int 
+sched_rr_interval(void)
+{
+	if (sched_quantum == 0)
+		sched_quantum = SCHED_QUANTUM;
+	return (sched_quantum);
+}
+
+/*
+ * We adjust the priority of the current process.  The priority of
+ * a process gets worse as it accumulates CPU time.  The cpu usage
+ * estimator (p_estcpu) is increased here.  resetpriority() will
+ * compute a different priority each time p_estcpu increases by
+ * INVERSE_ESTCPU_WEIGHT
+ * (until MAXPRI is reached).  The cpu usage estimator ramps up
+ * quite quickly when the process is running (linearly), and decays
+ * away exponentially, at a rate which is proportionally slower when
+ * the system is busy.  The basic principle is that the system will
+ * 90% forget that the process used a lot of CPU time in 5 * loadav
+ * seconds.  This causes the system to favor processes which haven't
+ * run much recently, and to round-robin among other processes.
+ */
+void
+sched_clock(struct thread *td)
+{
+	struct kse *ke;
+	struct ksegrp *kg;
+
+	KASSERT((td != NULL), ("schedclock: null thread pointer"));
+	ke = td->td_kse;
+	kg = td->td_ksegrp;
+	ke->ke_cpticks++;
+	kg->kg_estcpu = ESTCPULIM(kg->kg_estcpu + 1);
+	if ((kg->kg_estcpu % INVERSE_ESTCPU_WEIGHT) == 0) {
+		resetpriority(kg);
+		if (td->td_priority >= PUSER)
+			td->td_priority = kg->kg_user_pri;
+	}
+}
+/*
+ * charge childs scheduling cpu usage to parent.
+ *
+ * XXXKSE assume only one thread & kse & ksegrp keep estcpu in each ksegrp.
+ * Charge it to the ksegrp that did the wait since process estcpu is sum of
+ * all ksegrps, this is strictly as expected.  Assume that the child process
+ * aggregated all the estcpu into the 'built-in' ksegrp.
+ */
+void
+sched_exit(struct ksegrp *kg, struct ksegrp *child)
+{
+	kg->kg_estcpu = ESTCPULIM(kg->kg_estcpu + child->kg_estcpu);
+}
+
+void
+sched_fork(struct ksegrp *kg, struct ksegrp *child)
+{
+	/*
+	 * set priority of child to be that of parent.
+	 * XXXKSE this needs redefining..
+	 */     
+	child->kg_estcpu = kg->kg_estcpu;
+}
+
+void
+sched_nice(struct ksegrp *kg, int nice)
+{
+	kg->kg_nice = nice;
+	resetpriority(kg);
+}
+
+void
+sched_prio(struct thread *td, u_char prio)
+{
+	td->td_priority = prio;
+
+	if (TD_ON_RUNQ(td)) {
+		remrunqueue(td);
+		setrunqueue(td);
+	}
+}
+
+void
+sched_sleep(struct thread *td, u_char prio)
+{
+	td->td_ksegrp->kg_slptime = 0;
+	td->td_priority = prio;
+}
+
+void
+sched_switchin(struct thread *td)
+{
+	td->td_kse->ke_oncpu = PCPU_GET(cpuid);
+}
+
+void
+sched_switchout(struct thread *td)
+{
+	struct kse *ke;
+	struct proc *p;
+
+	ke = td->td_kse;
+	p = td->td_proc;
+
+	KASSERT((ke->ke_state == KES_THREAD), ("mi_switch: kse state?"));
+
+	td->td_lastcpu = ke->ke_oncpu;
+	ke->ke_oncpu = NOCPU;
+	ke->ke_flags &= ~KEF_NEEDRESCHED;
+	/*
+	 * At the last moment, if this thread is still marked RUNNING,
+	 * then put it back on the run queue as it has not been suspended
+	 * or stopped or any thing else similar.
+	 */
+	if (TD_IS_RUNNING(td)) {
+		/* Put us back on the run queue (kse and all). */
+		setrunqueue(td);
+	} else if (p->p_flag & P_KSES) {
+		/*
+		 * We will not be on the run queue. So we must be
+		 * sleeping or similar. As it's available,
+		 * someone else can use the KSE if they need it.
+		 * (If bound LOANING can still occur).
+		 */
+		kse_reassign(ke);
+	}
+}
+
+void
+sched_wakeup(struct thread *td)
+{
+	struct ksegrp *kg;
+
+	kg = td->td_ksegrp;
+	if (kg->kg_slptime > 1)
+		updatepri(kg);
+	kg->kg_slptime = 0;
+	setrunqueue(td);
+	maybe_resched(td);
+}
+
+void
+sched_add(struct kse *ke)
+{
+	mtx_assert(&sched_lock, MA_OWNED);
+	KASSERT((ke->ke_thread != NULL), ("runq_add: No thread on KSE"));
+	KASSERT((ke->ke_thread->td_kse != NULL),
+	    ("runq_add: No KSE on thread"));
+	KASSERT(ke->ke_state != KES_ONRUNQ,
+	    ("runq_add: kse %p (%s) already in run queue", ke,
+	    ke->ke_proc->p_comm));
+	KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
+	    ("runq_add: process swapped out"));
+	ke->ke_ksegrp->kg_runq_kses++;
+	ke->ke_state = KES_ONRUNQ;
+
+	runq_add(&runq, ke);
+}
+
+void
+sched_rem(struct kse *ke)
+{
+	KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
+	    ("runq_remove: process swapped out"));
+	KASSERT((ke->ke_state == KES_ONRUNQ), ("KSE not on run queue"));
+	mtx_assert(&sched_lock, MA_OWNED);
+
+	runq_remove(&runq, ke);
+	ke->ke_state = KES_THREAD;
+	ke->ke_ksegrp->kg_runq_kses--;
+}
+
+struct kse *
+sched_choose(void)
+{
+	struct kse *ke;
+
+	ke = runq_choose(&runq);
+
+	if (ke != NULL) {
+		runq_remove(&runq, ke);
+		ke->ke_state = KES_THREAD;
+
+		KASSERT((ke->ke_thread != NULL),
+		    ("runq_choose: No thread on KSE"));
+		KASSERT((ke->ke_thread->td_kse != NULL),
+		    ("runq_choose: No KSE on thread"));
+		KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
+		    ("runq_choose: process swapped out"));
+	}
+	return (ke);
+}
+
+void
+sched_userret(struct thread *td)
+{
+	struct ksegrp *kg;
+	/*
+	 * XXX we cheat slightly on the locking here to avoid locking in
+	 * the usual case.  Setting td_priority here is essentially an
+	 * incomplete workaround for not setting it properly elsewhere.
+	 * Now that some interrupt handlers are threads, not setting it
+	 * properly elsewhere can clobber it in the window between setting
+	 * it here and returning to user mode, so don't waste time setting
+	 * it perfectly here.
+	 */
+	kg = td->td_ksegrp;
+	if (td->td_priority != kg->kg_user_pri) {
+		mtx_lock_spin(&sched_lock);
+		td->td_priority = kg->kg_user_pri;
+		mtx_unlock_spin(&sched_lock);
+	}
+}