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SubjectRe: Still seeing decreasing stime/utime
* Peter Zijlstra <a.p.zijlstra@chello.nl> [2008-08-30 13:27:36]:

> On Sat, 2008-08-30 at 11:26 +0530, Balbir Singh wrote:
> > Spencer Candland wrote:
> > >> Here is an experimental patch (I've just compiled and booted a machine
> > >> with it, I am unable to reproduce your problem), could you please test
> > >> it for me and see if it helps solve the problem
> > >
> > > Looks like this fixed it. I have been testing this for the last 16
> > > hours and everything is looking good.
> > >
> >
> > Excellent! Ingo, Peter, do you like the patch? If so, could you please pick it
> > up Ingo. I think we should even push the fix to stable releases.
>
> Looks good, except for the issue you yourself earlier raised, a few of
> those functions looks too large to be inlined.
>

Here's the updated revision with task_*time functions moved to sched.c
and inlining removed, except for task_gtime(). I've compiled and
booted a machine (x86_64) with this patch applied.

Reported-by: spencer@bluehost.com

Spencer reported a problem where utime and stime were going negative despite
the fixes in commit b27f03d4bdc145a09fb7b0c0e004b29f1ee555fa. The suspected
reason for the problem is that signal_struct maintains it's own utime and
stime (of exited tasks), these are not updated using the new task_utime()
routine, hence sig->utime can go backwards and cause the same problem
to occur (sig->utime, adds tsk->utime and not task_utime()). This patch
fixes the problem

TODO: using max(task->prev_utime, derived utime) works for now, but a more
generic solution is to implement cputime_max() and use the cputime_gt()
function for comparison.

Comments?

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

fs/proc/array.c | 59 --------------------------------------------------
include/linux/sched.h | 4 +++
kernel/exit.c | 6 ++---
kernel/sched.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 66 insertions(+), 62 deletions(-)

diff -puN kernel/exit.c~fix-utime-stime-moving-backwards kernel/exit.c
--- linux-2.6.27-rc3/kernel/exit.c~fix-utime-stime-moving-backwards 2008-08-29 03:14:57.000000000 +0530
+++ linux-2.6.27-rc3-balbir/kernel/exit.c 2008-08-29 03:21:18.000000000 +0530
@@ -115,9 +115,9 @@ static void __exit_signal(struct task_st
* We won't ever get here for the group leader, since it
* will have been the last reference on the signal_struct.
*/
- sig->utime = cputime_add(sig->utime, tsk->utime);
- sig->stime = cputime_add(sig->stime, tsk->stime);
- sig->gtime = cputime_add(sig->gtime, tsk->gtime);
+ sig->utime = cputime_add(sig->utime, task_utime(tsk));
+ sig->stime = cputime_add(sig->stime, task_stime(tsk));
+ sig->gtime = cputime_add(sig->gtime, task_gtime(tsk));
sig->min_flt += tsk->min_flt;
sig->maj_flt += tsk->maj_flt;
sig->nvcsw += tsk->nvcsw;
diff -puN fs/proc/array.c~fix-utime-stime-moving-backwards fs/proc/array.c
--- linux-2.6.27-rc3/fs/proc/array.c~fix-utime-stime-moving-backwards 2008-08-29 03:14:58.000000000 +0530
+++ linux-2.6.27-rc3-balbir/fs/proc/array.c 2008-08-29 03:16:09.000000000 +0530
@@ -349,65 +349,6 @@ int proc_pid_status(struct seq_file *m,
return 0;
}

-/*
- * Use precise platform statistics if available:
- */
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
-static cputime_t task_utime(struct task_struct *p)
-{
- return p->utime;
-}
-
-static cputime_t task_stime(struct task_struct *p)
-{
- return p->stime;
-}
-#else
-static cputime_t task_utime(struct task_struct *p)
-{
- clock_t utime = cputime_to_clock_t(p->utime),
- total = utime + cputime_to_clock_t(p->stime);
- u64 temp;
-
- /*
- * Use CFS's precise accounting:
- */
- temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
-
- if (total) {
- temp *= utime;
- do_div(temp, total);
- }
- utime = (clock_t)temp;
-
- 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)
-{
- clock_t stime;
-
- /*
- * Use CFS's precise accounting. (we subtract utime from
- * the total, to make sure the total observed by userspace
- * grows monotonically - apps rely on that):
- */
- stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
- cputime_to_clock_t(task_utime(p));
-
- if (stime >= 0)
- p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
-
- return p->prev_stime;
-}
-#endif
-
-static cputime_t task_gtime(struct task_struct *p)
-{
- return p->gtime;
-}
-
static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task, int whole)
{
diff -puN include/linux/sched.h~fix-utime-stime-moving-backwards include/linux/sched.h
--- linux-2.6.27-rc3/include/linux/sched.h~fix-utime-stime-moving-backwards 2008-08-29 03:14:58.000000000 +0530
+++ linux-2.6.27-rc3-balbir/include/linux/sched.h 2008-08-30 18:43:56.000000000 +0530
@@ -1430,6 +1430,10 @@ static inline void put_task_struct(struc
__put_task_struct(t);
}

+extern cputime_t task_utime(struct task_struct *p);
+extern cputime_t task_stime(struct task_struct *p);
+extern cputime_t task_gtime(struct task_struct *p);
+
/*
* Per process flags
*/
diff -puN kernel/sched.c~fix-utime-stime-moving-backwards kernel/sched.c
--- linux-2.6.27-rc3/kernel/sched.c~fix-utime-stime-moving-backwards 2008-08-30 18:38:15.000000000 +0530
+++ linux-2.6.27-rc3-balbir/kernel/sched.c 2008-08-30 18:41:40.000000000 +0530
@@ -4176,6 +4176,65 @@ void account_steal_time(struct task_stru
}

/*
+ * Use precise platform statistics if available:
+ */
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+cputime_t task_utime(struct task_struct *p)
+{
+ return p->utime;
+}
+
+cputime_t task_stime(struct task_struct *p)
+{
+ return p->stime;
+}
+#else
+cputime_t task_utime(struct task_struct *p)
+{
+ clock_t utime = cputime_to_clock_t(p->utime),
+ total = utime + cputime_to_clock_t(p->stime);
+ u64 temp;
+
+ /*
+ * Use CFS's precise accounting:
+ */
+ temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
+
+ if (total) {
+ temp *= utime;
+ do_div(temp, total);
+ }
+ utime = (clock_t)temp;
+
+ p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
+ return p->prev_utime;
+}
+
+cputime_t task_stime(struct task_struct *p)
+{
+ clock_t stime;
+
+ /*
+ * Use CFS's precise accounting. (we subtract utime from
+ * the total, to make sure the total observed by userspace
+ * grows monotonically - apps rely on that):
+ */
+ stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
+ cputime_to_clock_t(task_utime(p));
+
+ if (stime >= 0)
+ p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
+
+ return p->prev_stime;
+}
+#endif
+
+inline cputime_t task_gtime(struct task_struct *p)
+{
+ return p->gtime;
+}
+
+/*
* This function gets called by the timer code, with HZ frequency.
* We call it with interrupts disabled.
*
_
--
Balbir


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