linux-kernel - Re: [PATCH 4/4] vtime: No need to disable irqs on vtime

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Date:	Wed, 14 Nov 2012 14:24:50 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH 4/4] vtime: No need to disable irqs on vtime_account()

On Wed, 2012-11-14 at 17:26 +0100, Frederic Weisbecker wrote:
> vtime_account() is only called from irq entry. irqs
> are always disabled at this point so we can safely
> remove the irq disabling guards on that function.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> ---
>  kernel/sched/cputime.c |    6 ------
>  1 files changed, 0 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 2e8d34a..80b2fd5 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -467,16 +467,10 @@ void vtime_task_switch(struct task_struct *prev)
>  #ifndef __ARCH_HAS_VTIME_ACCOUNT
>  void vtime_account(struct task_struct *tsk)
>  {
> -	unsigned long flags;
> -
> -	local_irq_save(flags);
> -

I'd add a WARN_ON_ONCE(!irqs_disabled()) again here, or is this also
covered by the vtime_delta()?

-- Steve

>  	if (in_interrupt() || !is_idle_task(tsk))
>  		vtime_account_system(tsk);
>  	else
>  		vtime_account_idle(tsk);
> -
> -	local_irq_restore(flags);
>  }
>  EXPORT_SYMBOL_GPL(vtime_account);
>  #endif /* __ARCH_HAS_VTIME_ACCOUNT */


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