Message-ID: <51F681E7.1060609@linaro.org>
Date: Mon, 29 Jul 2013 16:53:27 +0200
From: Daniel Lezcano <daniel.lezcano@linaro.org>
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To: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
CC: linuxppc-dev@lists.ozlabs.org, linux-pm@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [linux-pm] [PATCH 1/3] cpuidle/powernv: cpuidle backend driver
 for powernv
References: <20130723090111.7291.99479.stgit@deepthi.in.ibm.com> <20130723090137.7291.36657.stgit@deepthi.in.ibm.com> <51F35A2A.1080408@linaro.org> <51F67E96.6040008@linux.vnet.ibm.com>
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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@linux.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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