sched: keep utime/stime monotonic

keep utime/stime monotonic.

cpustats use utime/stime as a ratio against sum_exec_runtime, as a
consequence it can happen - when the ratio changes faster than time
accumulates - that either can be appear to go backwards.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 4 insertions, 1 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 63c95afb561f..d80baaabf835 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -358,7 +358,8 @@ static cputime_t task_utime(struct task_struct *p)
         }
         utime = (clock_t)temp;
 
-        return clock_t_to_cputime(utime);
+        p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
+        return p->prev_utime;
 }
 
 static cputime_t task_stime(struct task_struct *p)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3c07d595979f..b0b1fe6e0b17 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1009,6 +1009,7 @@ struct task_struct {
         unsigned int rt_priority;
         cputime_t utime, stime, utimescaled, stimescaled;
         cputime_t gtime;
+        cputime_t prev_utime;
         unsigned long nvcsw, nivcsw; /* context switch counts */
         struct timespec start_time;             /* monotonic time */
         struct timespec real_start_time;        /* boot based time */
diff --git a/kernel/fork.c b/kernel/fork.c
index ddafdfac9456..a65bfc47177c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1056,6 +1056,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         p->gtime = cputime_zero;
         p->utimescaled = cputime_zero;
         p->stimescaled = cputime_zero;
+        p->prev_utime = cputime_zero;
 
 #ifdef CONFIG_TASK_XACCT
         p->rchar = 0;           /* I/O counter: bytes read */