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Date: Sat, 30 Aug 2008 17:32:07 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: balbir@...ux.vnet.ibm.com
Cc: Spencer Candland <spencer@...ehost.com>,
dmitry.adamushko@...il.com, mingo@...e.hu,
linux-kernel@...r.kernel.org
Subject: Re: Still seeing decreasing stime/utime
On Sat, 2008-08-30 at 19:25 +0530, Balbir Singh wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.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@...ehost.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@...ux.vnet.ibm.com>
Thanks Balbir!
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>
> 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.
> *
> _
>
--
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