linux-kernel - Re: [PATCH V2 3/3] workqueue: Schedule work on non-idle cpu instead of current one

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Message-ID: <CAKohpon2xQxSqeOCTb=noki=QUH=Cf9Aggsd_uAv34TNfyC0FA@mail.gmail.com>
Date:	Sun, 30 Sep 2012 17:46:45 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, pjt@...gle.com,
	paul.mckenney@...aro.org, tglx@...utronix.de,
	suresh.b.siddha@...el.com, venki@...gle.com, mingo@...hat.com,
	peterz@...radead.org, robin.randhawa@....com,
	Steve.Bannister@....com, Arvind.Chauhan@....com,
	amit.kucheria@...aro.org, vincent.guittot@...aro.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org
Subject: Re: [PATCH V2 3/3] workqueue: Schedule work on non-idle cpu instead
 of current one

On 30 September 2012 14:24, Tejun Heo <tj@...nel.org> wrote:
> On Thu, Sep 27, 2012 at 02:34:05PM +0530, Viresh Kumar wrote:
>> - A cpu has programmed a timer and is IDLE now.
>> - CPU gets into interrupt handler due to timer and queues a work. As the CPU is
>>   currently IDLE, we can queue this work to some other CPU.
>
> I'm still a bit confused, if the CPU is already running the IRQ
> handler, the CPU is not idle by definition.  What am I missing here?

Hi Tejun,

For the scheduler CPU is idle, if all below are true:
- current task is idle task
- nr_running == 0
- wake_list is empty

And during these conditions, there can be a timer running in background.
And when we reach its interrupt handler, then also these conditions hold true
and local cpu is idle.

--
Viresh
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