--- //depot/projects/smpng/sys/kern/kern_shutdown.c	2009/04/07 17:48:51
+++ //depot/user/jhb/preemption/kern/kern_shutdown.c	2009/04/07 19:19:09
@@ -56,6 +56,7 @@
 #include <sys/kerneldump.h>
 #include <sys/kthread.h>
 #include <sys/malloc.h>
+#include <sys/ktr.h>
 #include <sys/mount.h>
 #include <sys/priv.h>
 #include <sys/proc.h>
@@ -297,6 +298,10 @@
 	 */
 	EVENTHANDLER_INVOKE(shutdown_pre_sync, howto);
 
+	KASSERT(curthread->td_critnest == 0, ("boot called from a critical section"));
+#ifdef __i386__
+	KASSERT((read_eflags() & PSL_I), ("boot called with interrupts disabled"));
+#endif
 	/* 
 	 * Now sync filesystems
 	 */
--- //depot/projects/smpng/sys/kern/kern_synch.c	2009/02/27 15:49:22
+++ //depot/user/jhb/preemption/kern/kern_synch.c	2009/02/27 16:32:01
@@ -377,6 +377,14 @@
 	panic("%s: did not reenter debugger", __func__);
 }
 
+u_long preempt_switches, total_switches;
+
+SYSCTL_NODE(_debug, OID_AUTO, switches, CTLFLAG_RD, NULL, "switch counts");
+SYSCTL_ULONG(_debug_switches, OID_AUTO, total, CTLFLAG_RD, &total_switches, 0,
+    "");
+SYSCTL_ULONG(_debug_switches, OID_AUTO, preempt, CTLFLAG_RD, &preempt_switches,
+    0, "");
+
 /*
  * The machine independent parts of context switching.
  */
@@ -408,10 +416,13 @@
 	 */
 	if (kdb_active)
 		kdb_switch();
+	total_switches++;
 	if (flags & SW_VOL)
 		td->td_ru.ru_nvcsw++;
-	else
+	else {
 		td->td_ru.ru_nivcsw++;
+		preempt_switches++;
+	}
 #ifdef SCHED_STATS
 	SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
 #endif
--- //depot/projects/smpng/sys/notes	2009/02/18 22:05:55
+++ //depot/user/jhb/preemption/notes	2009/02/20 16:15:34
@@ -73,3 +73,22 @@
 - jhb_socket - socket hacking
 
 Space reserved for child branches:
++ Disable preemption when waking up several threads until they are all woken
+  up.
+  - Testing
++ Fixup some things that are really curthread only
+  - Testing
+- Testing
+  - x86 UP
+    - corrupted eip's on returns from faults (seem to be off by one? for
+      both userland and kernel)
+  - x86 SMP
+  - alpha
+  - sparc64
+  - amd64
+  - ia64
+- possibly stash the thread we should preempt to in a per-cpu variable while
+  in a critical section so that critical_exit() can avoid calling
+  choosethread()?
+  - we would have to defer the setrunqueue for this to work, that may not be
+    a good idea
--- //depot/projects/smpng/sys/vm/vm_glue.c	2008/08/05 21:26:01
+++ //depot/user/jhb/preemption/vm/vm_glue.c	2008/08/06 17:00:06
@@ -642,6 +642,7 @@
 		FOREACH_THREAD_IN_PROC(p, td)
 			vm_thread_swapin(td);
 		PROC_LOCK(p);
+		critical_enter();
 		swapclear(p);
 		p->p_swtick = ticks;
 
@@ -649,6 +650,7 @@
 
 		/* Allow other threads to swap p out now. */
 		--p->p_lock;
+		critical_exit();
 	}
 #endif /* NO_SWAPPING */
 }