Index: kern_synch.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_synch.c,v
retrieving revision 1.239
diff -u -r1.239 kern_synch.c
--- kern_synch.c	25 Jan 2004 07:49:45 -0000	1.239
+++ kern_synch.c	25 Jan 2004 09:15:56 -0000
@@ -453,7 +453,6 @@
 void
 mi_switch(int flags)
 {
-	struct bintime new_switchtime;
 	struct thread *td;
 	struct proc *p;
 
@@ -469,21 +468,6 @@
 	    ("mi_switch: switch in a critical section"));
 	KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
 	    ("mi_switch: switch must be voluntary or involuntary"));
-
-	if (flags & SW_VOL)
-		p->p_stats->p_ru.ru_nvcsw++;
-	else
-		p->p_stats->p_ru.ru_nivcsw++;
-	/*
-	 * Compute the amount of time during which the current
-	 * process was running, and add that to its total so far.
-	 */
-	binuptime(&new_switchtime);
-	bintime_add(&p->p_runtime, &new_switchtime);
-	bintime_sub(&p->p_runtime, PCPU_PTR(switchtime));
-
-	td->td_generation++;	/* bump preempt-detect counter */
-
 #ifdef DDB
 	/*
 	 * Don't perform context switches from the debugger.
@@ -494,23 +478,42 @@
 		db_error("Context switches not allowed in the debugger");
 	}
 #endif
-
 	/*
-	 * Check if the process exceeds its cpu resource allocation.  If
-	 * over max, arrange to kill the process in ast().
+	 * Compute rusage information.  This is skipped for kthreads to avoid
+	 * the cost of the timer operations.  We clear switchticks to let the
+	 * incoming thread know that switchtime and switchticks are not valid.
 	 */
-	if (p->p_cpulimit != RLIM_INFINITY &&
-	    p->p_runtime.sec > p->p_cpulimit) {
-		p->p_sflag |= PS_XCPU;
-		td->td_flags |= TDF_ASTPENDING;
-	}
+	if ((p->p_flag & P_KTHREAD) == 0) {
+		struct bintime new_switchtime;
 
+		if (flags & SW_VOL)
+			p->p_stats->p_ru.ru_nvcsw++;
+		else
+			p->p_stats->p_ru.ru_nivcsw++;
+		/*
+		 * Compute the amount of time during which the current
+		 * process was running, and add that to its total so far.
+		 */
+		binuptime(&new_switchtime);
+		bintime_add(&p->p_runtime, &new_switchtime);
+		bintime_sub(&p->p_runtime, PCPU_PTR(switchtime));
+		PCPU_SET(switchtime, new_switchtime);
+		/*
+		 * Check if the process exceeds its cpu resource allocation.
+		 * If over max, arrange to kill the process in ast().
+		 */
+		if (p->p_cpulimit != RLIM_INFINITY &&
+		    p->p_runtime.sec > p->p_cpulimit) {
+			p->p_sflag |= PS_XCPU;
+			td->td_flags |= TDF_ASTPENDING;
+		}
+	} else
+		PCPU_SET(switchticks, 0);
 	/*
 	 * Finish up stats for outgoing thread.
 	 */
+	td->td_generation++;	/* bump preempt-detect counter */
 	cnt.v_swtch++;
-	PCPU_SET(switchtime, new_switchtime);
-	PCPU_SET(switchticks, ticks);
 	CTR3(KTR_PROC, "mi_switch: old thread %p (pid %d, %s)", td, p->p_pid,
 	    p->p_comm);
 	if (td->td_proc->p_flag & P_SA)
@@ -519,6 +522,19 @@
 
 	CTR3(KTR_PROC, "mi_switch: new thread %p (pid %d, %s)", td, p->p_pid,
 	    p->p_comm);
+
+	/*
+	 * If the incoming thread is not a kthread and the last thread didn't
+	 * update switchtime, we must set it here to keep accurate rusage
+	 * statistics.
+	 */
+	if ((p->p_flag & P_KTHREAD) == 0 &&
+	    PCPU_GET(switchticks) == 0) {
+		struct bintime new_switchtime;
+		binuptime(&new_switchtime);
+		PCPU_SET(switchtime, new_switchtime);
+	}
+	PCPU_SET(switchticks, ticks);
 
 	/* 
 	 * If the last thread was exiting, finish cleaning it up.