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

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Date:	Tue, 23 Oct 2012 14:34:21 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

2012/10/22 Peter Zijlstra <peterz@...radead.org>:
> 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.

Good point! I need to send an ipi in that case. Will fix on the next version.

Thanks.
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