linux-kernel - Re: [linux-pm] [PATCH 1/3] cpuidle/powernv: cpuidle backend driver for powernv

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Date:	Mon, 29 Jul 2013 16:53:27 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
CC:	linuxppc-dev@...ts.ozlabs.org, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] [PATCH 1/3] cpuidle/powernv: cpuidle backend driver
 for powernv

On 07/29/2013 04:39 PM, Deepthi Dharwar wrote:
> Hi Daniel,
> 
> On 07/27/2013 10:57 AM, Daniel Lezcano wrote:
>> On 07/23/2013 11:01 AM, Deepthi Dharwar wrote:
>>> This patch implements a back-end cpuidle driver for
>>> powernv calling power7_nap and snooze idle states.
>>> This can be extended by adding more idle states
>>> in the future to the existing framework.
>>>
>>> Signed-off-by: Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>

[ ... ]

>>> +static int snooze_loop(struct cpuidle_device *dev,
>>> +			struct cpuidle_driver *drv,
>>> +			int index)
>>> +{
>>> +	int cpu = dev->cpu;
>>> +
>>> +	local_irq_enable();
>>> +	set_thread_flag(TIF_POLLING_NRFLAG);
>>> +
>>> +	while ((!need_resched()) && cpu_online(cpu)) {
>>> +		ppc64_runlatch_off();
>>> +		HMT_very_low();
>>> +	}
>>
>> Why are you using the cpu_online test here ?
> 
> Snooze state is an idle state where cpu executes an infinite loop by
> reducing the priority of the thread and the idle cpu can come out of it
> only if need_resched is set or in case the cpu is offlined. In order to
> continue executing this loop to remain in this idle state, we need the
> check just to be safe.

Yes, but if the cpu is offline you are no longer executing this code, no ?

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