linux-kernel - Re: [PATCH 04/33] cputime: Allow dynamic switch between tick/virtual based cputime accounting

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Date:	Tue, 08 Jan 2013 16:20:56 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 04/33] cputime: Allow dynamic switch between
 tick/virtual based cputime accounting

On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:

> @@ -439,29 +443,13 @@ void account_idle_ticks(unsigned long ticks)
>  
>  	account_idle_time(jiffies_to_cputime(ticks));
>  }
> -
>  #endif
>  
> +

Spurious newline.

-- Steve

>  /*
>   * Use precise platform statistics if available:
>   */
>  #ifdef CONFIG_VIRT_CPU_ACCOUNTING
> -void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
> -{
> -	*ut = p->utime;
> -	*st = p->stime;
> -}
> -
> -void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
> -{
> -	struct task_cputime cputime;
> -
> -	thread_group_cputime(p, &cputime);
> -
> -	*ut = cputime.utime;
> -	*st = cputime.stime;
> -}
> -
>  void vtime_account_system_irqsafe(struct task_struct *tsk)
>  {
>  	unsigned long flags;
> @@ -517,8 +505,25 @@ void vtime_account(struct task_struct *tsk)
>  }
>  EXPORT_SYMBOL_GPL(vtime_account);
>  #endif /* __ARCH_HAS_VTIME_ACCOUNT */
> +#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
>  
> -#else
> +#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
> +void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
> +{
> +	*ut = p->utime;
> +	*st = p->stime;
> +}

Why not keep this out in the open like:

static void __task_cputime_adjusted() {
	...
}

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
void task_cputime_adjusted(...)
{
	__task_cputime_adjusted(p, ut, st);
}

> +
> +void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
> +{
> +	struct task_cputime cputime;
> +
> +	thread_group_cputime(p, &cputime);
> +
> +	*ut = cputime.utime;
> +	*st = cputime.stime;
> +}
> +#else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
>  
>  #ifndef nsecs_to_cputime
>  # define nsecs_to_cputime(__nsecs)	nsecs_to_jiffies(__nsecs)
> @@ -548,6 +553,12 @@ static void cputime_adjust(struct task_cputime *curr,
>  {
>  	cputime_t rtime, utime, total;
>  
> +	if (vtime_accounting_enabled()) {
> +		*ut = curr->utime;
> +		*st = curr->stime;

Then here, we can do:

		__task_cputime_adjusted(curr, ut, st);
> +		return;

Isn't suppose to do basically the same thing, when
vtime_accounting_enabled() is set?

> +	}
> +
>  	utime = curr->utime;
>  	total = utime + curr->stime;
>  
> @@ -601,7 +612,7 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
>  	thread_group_cputime(p, &cputime);
>  	cputime_adjust(&cputime, &p->signal->prev_cputime, ut, st);
>  }
> -#endif
> +#endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
>  
>  #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
>  static DEFINE_PER_CPU(long, last_jiffies) = INITIAL_JIFFIES;
> @@ -643,6 +654,11 @@ void vtime_account_idle(struct task_struct *tsk)
>  	account_idle_time(delta_cpu);
>  }
>  
> +bool vtime_accounting_enabled(void)
> +{
> +	return context_tracking_active();
> +}
> +
>  static int __cpuinit vtime_cpu_notify(struct notifier_block *self,
>  				      unsigned long action, void *hcpu)
>  {
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index fb8e5e4..314b9ee 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -632,8 +632,11 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
>  
>  static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
>  {
> -#ifndef CONFIG_VIRT_CPU_ACCOUNTING
> +#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
>  	unsigned long ticks;
> +
> +	if (vtime_accounting_enabled())
> +		return;

If this can be dynamically changed at runtime, wouldn't some of these
accounting variables get corrupted? Like the last_jiffies per_cpu
variable?

-- Steve

>  	/*
>  	 * We stopped the tick in idle. Update process times would miss the
>  	 * time we slept as update_process_times does only a 1 tick


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