sched: fix prev_stime calculation

Srivatsa Vaddagiri noticed occasionally incorrect CPU usage values in top and tracked it down to stime going below 0 in task_stime(). Negative values are possible there due to the sampled nature of stime/utime. Fix suggested by Balbir Singh. Signed-off-by: Ingo Molnar <[email protected]> Tested-by: Srivatsa Vaddagiri <[email protected]> Reviewed-by: Balbir Singh <[email protected]>
kishon · Nov 26, 2007 · 08e4570 · 08e4570
1 parent 5e8869b
commit 08e4570
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/fs/proc/array.c b/fs/proc/array.c
@@ -374,7 +374,9 @@ static cputime_t task_stime(struct task_struct *p)
 	stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
 			cputime_to_clock_t(task_utime(p));
 
-	p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+	if (stime >= 0)
+		p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+
 	return p->prev_stime;
 }
 #endif