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

Balbir Singh
2007-10-29T22:13:40Z

On Mon, Oct 29, 2007 at 09:04:25PM +0100, Ingo Molnar wrote:
>
> * 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
>

We'll also need this additional patch (untested), but in the long run
I think the approach needs to be

1. Update stime and utime at the time of context switching -- keep it
in sync with p->sum_exec_runtime
2. Keep track of system/user context at system call entry points

Extend Peter's patch to fix accounting issues.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

fs/proc/array.c | 3 ++-
include/linux/sched.h | 2 +-
kernel/fork.c | 1 +
3 files changed, 4 insertions(+), 2 deletions(-)

diff -puN fs/proc/array.c~fix-accounting-issue-extended fs/proc/array.c
--- 2.6.24-rc1/fs/proc/array.c~fix-accounting-issue-extended 2007-10-30 03:08:18.000000000 +0530
+++ 2.6.24-rc1-balbir/fs/proc/array.c 2007-10-30 03:09:46.000000000 +0530
@@ -374,7 +374,8 @@ static cputime_t task_stime(struct task_
stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
cputime_to_clock_t(task_utime(p));

- return clock_t_to_cputime(stime);
+ p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+ return p->prev_stime;
}
#endif

diff -puN include/linux/sched.h~fix-accounting-issue-extended include/linux/sched.h
--- 2.6.24-rc1/include/linux/sched.h~fix-accounting-issue-extended 2007-10-30 03:08:18.000000000 +0530
+++ 2.6.24-rc1-balbir/include/linux/sched.h 2007-10-30 03:08:32.000000000 +0530
@@ -1004,7 +1004,7 @@ struct task_struct {
unsigned int rt_priority;
cputime_t utime, stime, utimescaled, stimescaled;
cputime_t gtime;
- cputime_t prev_utime;
+ cputime_t prev_utime, prev_stime;
unsigned long nvcsw, nivcsw; /* context switch counts */
struct timespec start_time; /* monotonic time */
struct timespec real_start_time; /* boot based time */
diff -puN kernel/fork.c~fix-accounting-issue-extended kernel/fork.c
--- 2.6.24-rc1/kernel/fork.c~fix-accounting-issue-extended 2007-10-30 03:08:18.000000000 +0530
+++ 2.6.24-rc1-balbir/kernel/fork.c 2007-10-30 03:08:42.000000000 +0530
@@ -1057,6 +1057,7 @@ static struct task_struct *copy_process(
p->utimescaled = cputime_zero;
p->stimescaled = cputime_zero;
p->prev_utime = cputime_zero;
+ p->prev_stime = cputime_zero;

#ifdef CONFIG_TASK_XACCT
p->rchar = 0; /* I/O counter: bytes read */
_

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL