linux-kernel - Re: [PATCH 2/2] timer: really raise softirq if there is irq

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Message-ID: <20140131121104.382942cc@gandalf.local.home>
Date:	Fri, 31 Jan 2014 12:11:04 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 2/2] timer: really raise softirq if there is irq_work to
 do

On Fri, 31 Jan 2014 12:07:57 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index 106968f..426d114 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1461,18 +1461,20 @@ void run_local_timers(void)
>  	 * the timer softirq.
>  	 */
>  #ifdef CONFIG_PREEMPT_RT_FULL
> +	/* On RT, irq work runs from softirq */
> +	if (irq_work_needs_cpu()) {
> +		raise_softirq(TIMER_SOFTIRQ);
> +		return;
> +	}
> +
>  	if (!spin_do_trylock(&base->lock)) {
>  		raise_softirq(TIMER_SOFTIRQ);
>  		return;
>  	}
>  #endif

Note, I debated about doing:

	if (irq_work_needs_cpu() ||
	    !spin_do_trylock(&base->lock)) {
		raise_softirq(TIMER_SOFTIRQ);
		return;
	}

instead, which is pretty much the same code. But I find it rather ugly,
and does not read as well. I haven't looked at the disassembly, but I
would hope that gcc would make my original version have the same result
as this one.

-- Steve
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