linux-kernel - Re: [RFC PATCH 5/8] irq_work: Make self-IPIs optable

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Date:	Mon, 22 Oct 2012 12:41:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [RFC PATCH 5/8] irq_work: Make self-IPIs optable

On Sat, 2012-10-20 at 12:22 -0400, Frederic Weisbecker wrote:
> +       if (empty) {
> +               /*
> +                * If an IPI is requested, raise it right away. Otherwise wait
> +                * for the next tick unless it's stopped. Now if the arch uses
> +                * some other obscure way than IPI to raise an irq work, just raise
> +                * and don't think further.
> +                */
> +               if (ipi || !arch_irq_work_has_ipi() || tick_nohz_tick_stopped())
> +                       arch_irq_work_raise();
> +       }
>         preempt_enable();
>  } 

Doesn't this have a problem where we enqueue the first lazy and then one
with ipi? In that case it appears we won't send the IPI because the
queue wasn't empty.


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