From c975a5d3594c900588a145e7dddea2f808cfe131 Mon Sep 17 00:00:00 2001
From: Conrad Meyer <cem@FreeBSD.org>
Date: Fri, 25 Mar 2016 19:35:29 +0000
Subject: [PATCH] Add td_swinvoltick to track last involuntary context switch

Expose in DDB via "show thread."

Reviewed by:	markj
Sponsored by:	EMC / Isilon Storage Division
---
 sys/ddb/db_ps.c       | 12 ++++++++++++
 sys/kern/kern_synch.c |  4 +++-
 sys/sys/proc.h        |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/sys/ddb/db_ps.c b/sys/ddb/db_ps.c
index f38c89fe7ae..76ab2c58624 100644
--- a/sys/ddb/db_ps.c
+++ b/sys/ddb/db_ps.c
@@ -36,6 +36,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/cons.h>
 #include <sys/jail.h>
 #include <sys/kdb.h>
+#include <sys/kernel.h>
 #include <sys/proc.h>
 #include <sys/sysent.h>
 #include <sys/systm.h>
@@ -302,6 +303,7 @@ DB_SHOW_COMMAND(thread, db_show_thread)
 	struct thread *td;
 	struct lock_object *lock;
 	bool comma;
+	int delta;
 
 	/* Determine which thread to examine. */
 	if (have_addr)
@@ -376,6 +378,16 @@ DB_SHOW_COMMAND(thread, db_show_thread)
 		    td->td_wchan);
 	db_printf(" priority: %d\n", td->td_priority);
 	db_printf(" container lock: %s (%p)\n", lock->lo_name, lock);
+	if (td->td_swvoltick != 0) {
+		delta = (u_int)ticks - (u_int)td->td_swvoltick;
+		db_printf(" last voluntary switch: %d ms ago\n",
+		    1000 * delta / hz);
+	}
+	if (td->td_swinvoltick != 0) {
+		delta = (u_int)ticks - (u_int)td->td_swinvoltick;
+		db_printf(" last involuntary switch: %d ms ago\n",
+		    1000 * delta / hz);
+	}
 }
 
 DB_SHOW_COMMAND(proc, db_show_proc)
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 8c847736f9d..432312e761a 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -438,8 +438,10 @@ mi_switch(int flags, struct thread *newtd)
 	if (flags & SW_VOL) {
 		td->td_ru.ru_nvcsw++;
 		td->td_swvoltick = ticks;
-	} else
+	} else {
 		td->td_ru.ru_nivcsw++;
+		td->td_swinvoltick = ticks;
+	}
 #ifdef SCHED_STATS
 	SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
 #endif
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 5d96406b875..2d1769e4309 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -254,6 +254,7 @@ struct thread {
 	int		td_slptick;	/* (t) Time at sleep. */
 	int		td_blktick;	/* (t) Time spent blocked. */
 	int		td_swvoltick;	/* (t) Time at last SW_VOL switch. */
+	int		td_swinvoltick;	/* (t) Time at last SW_INVOL switch. */
 	u_int		td_cow;		/* (*) Number of copy-on-write faults */
 	struct rusage	td_ru;		/* (t) rusage information. */
 	struct rusage_ext td_rux;	/* (t) Internal rusage information. */