[PATCH] add context switch counters

From: Peter Chubb <peterc@gelato.unsw.edu.au>

Currently, the context switch counters reported by getrusage() are
always zero.  The appended patch adds fields to struct task_struct to
count context switches, and adds code to do the counting.

The patch adds 4 longs to struct task struct, and a single addition to
the fast path in schedule().

include/linux/sched.h

@@ -391,6 +391,7 @@ struct task_struct {
 	struct timer_list real_timer;
 	struct list_head posix_timers; /* POSIX.1b Interval Timers */
 	unsigned long utime, stime, cutime, cstime;
+	unsigned long nvcsw, nivcsw, cnvcsw, cnivcsw; /* context switch counts */
 	u64 start_time;
 /* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
 	unsigned long min_flt, maj_flt, nswap, cmin_flt, cmaj_flt, cnswap;

kernel/exit.c

@@ -80,6 +80,8 @@ void release_task(struct task_struct * p)
 	p->parent->cmin_flt += p->min_flt + p->cmin_flt;
 	p->parent->cmaj_flt += p->maj_flt + p->cmaj_flt;
 	p->parent->cnswap += p->nswap + p->cnswap;
+	p->parent->cnvcsw += p->nvcsw + p->cnvcsw;
+	p->parent->cnivcsw += p->nivcsw + p->cnivcsw;
 	sched_exit(p);
 	write_unlock_irq(&tasklist_lock);
 	spin_unlock(&p->proc_lock);

kernel/fork.c

@@ -461,6 +461,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
 	tsk->min_flt = tsk->maj_flt = 0;
 	tsk->cmin_flt = tsk->cmaj_flt = 0;
 	tsk->nswap = tsk->cnswap = 0;
+	tsk->nvcsw = tsk->nivcsw = tsk->cnvcsw = tsk->cnivcsw = 0;
 
 	tsk->mm = NULL;
 	tsk->active_mm = NULL;

kernel/sched.c

@@ -1325,8 +1325,10 @@ asmlinkage void schedule(void)
 		}
 	default:
 		deactivate_task(prev, rq);
+		prev->nvcsw++;
+		break;
 	case TASK_RUNNING:
-		;
+		prev->nivcsw++;
 	}
 pick_next_task:
 	if (unlikely(!rq->nr_running)) {

kernel/sys.c

@@ -1309,6 +1309,8 @@ int getrusage(struct task_struct *p, int who, struct rusage __user *ru)
 		case RUSAGE_SELF:
 			jiffies_to_timeval(p->utime, &r.ru_utime);
 			jiffies_to_timeval(p->stime, &r.ru_stime);
+			r.ru_nvcsw = p->nvcsw;
+			r.ru_nivcsw = p->nivcsw;
 			r.ru_minflt = p->min_flt;
 			r.ru_majflt = p->maj_flt;
 			r.ru_nswap = p->nswap;
@@ -1316,6 +1318,8 @@ int getrusage(struct task_struct *p, int who, struct rusage __user *ru)
 		case RUSAGE_CHILDREN:
 			jiffies_to_timeval(p->cutime, &r.ru_utime);
 			jiffies_to_timeval(p->cstime, &r.ru_stime);
+			r.ru_nvcsw = p->cnvcsw;
+			r.ru_nivcsw = p->cnivcsw;
 			r.ru_minflt = p->cmin_flt;
 			r.ru_majflt = p->cmaj_flt;
 			r.ru_nswap = p->cnswap;
@@ -1323,6 +1327,8 @@ int getrusage(struct task_struct *p, int who, struct rusage __user *ru)
 		default:
 			jiffies_to_timeval(p->utime + p->cutime, &r.ru_utime);
 			jiffies_to_timeval(p->stime + p->cstime, &r.ru_stime);
+			r.ru_nvcsw = p->nvcsw + p->cnvcsw;
+			r.ru_nivcsw = p->nivcsw + p->cnivcsw;
 			r.ru_minflt = p->min_flt + p->cmin_flt;
 			r.ru_majflt = p->maj_flt + p->cmaj_flt;
 			r.ru_nswap = p->nswap + p->cnswap;