Re: [stable] 2.6.23 regression: top displaying 9999% CPU usage

Ingo Molnar
2007-10-29T20:05:18Z

* Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> We'll I initially thought of it and then I remembered that the
> regression occurs only when the accounting itself is inaccurate. I am
> tempted to ack the removal, but I would like to get input from others.
> Meanwhile, I'll try and see if I can fix the problem

i've got a patch from Peter queued up. (see below) This should fix the
main issue.

Ingo

-------------------->
Subject: sched: keep utime/stime monotonic
From: Peter Zijlstra <a.p.zijlstra@chello.nl>

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>
---
fs/proc/array.c | 3 ++-
include/linux/sched.h | 1 +
kernel/fork.c | 1 +
3 files changed, 4 insertions(+), 1 deletion(-)

Index: linux/fs/proc/array.c
===================================================================
--- linux.orig/fs/proc/array.c
+++ linux/fs/proc/array.c
@@ -358,7 +358,8 @@ static cputime_t task_utime(struct task_
}
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)
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/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 */
Index: linux/kernel/fork.c
===================================================================
--- linux.orig/kernel/fork.c
+++ linux/kernel/fork.c
@@ -1056,6 +1056,7 @@ static struct task_struct *copy_process(
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 */