Move dead procs to the reaper queue immediately after context switch.

This eliminates a forced context switch to the idle proc. In addition,
sched_exit() no longer needs to sum proc runtime because mi_switch()
will do it.

OK mpi@ a while ago

3 files changed, 23 insertions, 31 deletions

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index ab2f0de086d..570aa737f2f 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_exit.c,v 1.178 2019/06/21 09:39:48 visa Exp $	*/
+/*	$OpenBSD: kern_exit.c,v 1.179 2019/11/02 05:31:20 visa Exp $	*/
 /*	$NetBSD: kern_exit.c,v 1.39 1996/04/22 01:38:25 christos Exp $	*/
 
 /*
@@ -367,21 +367,27 @@ struct mutex deadproc_mutex =
 struct proclist deadproc = LIST_HEAD_INITIALIZER(deadproc);
 
 /*
- * We are called from cpu_exit() once it is safe to schedule the
- * dead process's resources to be freed.
+ * Move dead procs from the CPU's local list to the reaper list and
+ * wake up the reaper.
  *
- * NOTE: One must be careful with locking in this routine.  It's
- * called from a critical section in machine-dependent code, so
- * we should refrain from changing any interrupt state.
- *
- * We lock the deadproc list, place the proc on that list (using
- * the p_hash member), and wake up the reaper.
+ * This is called once it is safe to free the resources of dead processes.
  */
 void
-exit2(struct proc *p)
+dispatch_deadproc(void)
 {
+	struct proc *dead;
+	struct schedstate_percpu *spc = &curcpu()->ci_schedstate;
+
+	if (LIST_EMPTY(&spc->spc_deadproc))
+		return;
+
+	KERNEL_ASSERT_UNLOCKED();
+
 	mtx_enter(&deadproc_mutex);
-	LIST_INSERT_HEAD(&deadproc, p, p_hash);
+	while ((dead = LIST_FIRST(&spc->spc_deadproc)) != NULL) {
+		LIST_REMOVE(dead, p_hash);
+		LIST_INSERT_HEAD(&deadproc, dead, p_hash);
+	}
 	mtx_leave(&deadproc_mutex);
 
 	wakeup(&deadproc);
diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
index a32dbba110d..94ebd833ab1 100644
--- a/sys/kern/kern_sched.c
+++ b/sys/kern/kern_sched.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sched.c,v 1.60 2019/11/01 20:58:01 mpi Exp $	*/
+/*	$OpenBSD: kern_sched.c,v 1.61 2019/11/02 05:31:20 visa Exp $	*/
 /*
  * Copyright (c) 2007, 2008 Artur Grabowski <art@openbsd.org>
  *
@@ -159,17 +159,10 @@ sched_idle(void *v)
 
 	while (1) {
 		while (!cpu_is_idle(curcpu())) {
-			struct proc *dead;
-
 			SCHED_LOCK(s);
 			p->p_stat = SSLEEP;
 			mi_switch();
 			SCHED_UNLOCK(s);
-
-			while ((dead = LIST_FIRST(&spc->spc_deadproc))) {
-				LIST_REMOVE(dead, p_hash);
-				exit2(dead);
-			}
 		}
 
 		splassert(IPL_NONE);
@@ -204,7 +197,7 @@ sched_idle(void *v)
  * and waking up the reaper without risking having our address space and
  * stack torn from under us before we manage to switch to another proc.
  * Therefore we have a per-cpu list of dead processes where we put this
- * proc and have idle clean up that list and move it to the reaper list.
+ * proc. We move the list to the reaper list after context switch.
  * All this will be unnecessary once we can bind the reaper this cpu
  * and not risk having it switch to another in case it sleeps.
  */
@@ -212,14 +205,8 @@ void
 sched_exit(struct proc *p)
 {
 	struct schedstate_percpu *spc = &curcpu()->ci_schedstate;
-	struct timespec ts;
-	struct proc *idle;
 	int s;
 
-	nanouptime(&ts);
-	timespecsub(&ts, &spc->spc_runtime, &ts);
-	timespecadd(&p->p_rtime, &ts, &p->p_rtime);
-
 	LIST_INSERT_HEAD(&spc->spc_deadproc, p, p_hash);
 
 #ifdef MULTIPROCESSOR
@@ -229,10 +216,8 @@ sched_exit(struct proc *p)
 #endif
 
 	SCHED_LOCK(s);
-	idle = spc->spc_idleproc;
-	idle->p_stat = SRUN;
-	cpu_switchto(NULL, idle);
-	panic("cpu_switchto returned");
+	mi_switch();
+	panic("mi_switch returned");
 }
 
 /*
diff --git a/sys/kern/sched_bsd.c b/sys/kern/sched_bsd.c
index c237dac5bad..8f988ae7c57 100644
--- a/sys/kern/sched_bsd.c
+++ b/sys/kern/sched_bsd.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sched_bsd.c,v 1.57 2019/11/01 20:58:01 mpi Exp $	*/
+/*	$OpenBSD: sched_bsd.c,v 1.58 2019/11/02 05:31:20 visa Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*-
@@ -413,6 +413,7 @@ mi_switch(void)
 
 	SCHED_ASSERT_UNLOCKED();
 
+	dispatch_deadproc();
 	smr_idle();
 
 	/*