linux-kernel - Re: [PATCH 2/2] cpuidle / menu: Return error code if there are no suitable states

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Date:	Wed, 30 Apr 2014 14:40:31 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] cpuidle / menu: Return error code if there are no
 suitable states

On 04/29/2014 01:28 AM, Rafael J. Wysocki wrote:
> On Monday, April 28, 2014 01:14:32 PM Daniel Lezcano wrote:
>> On 04/27/2014 02:55 PM, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>
>>> If there is a PM QoS latency limit and all of the sufficiently shallow
>>> C-states are disabled, the cpuidle menu governor returns 0 which on
>>> some systems is CPUIDLE_DRIVER_STATE_START and shouldn't be returned
>>> if that C-state has been disabled.
>>>
>>> Fix the issue by modifying the menu governor to return an error code
>>> in such situations.
>>>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>> ---
>>>    drivers/cpuidle/governors/menu.c |    2 +-
>>>    include/linux/cpuidle.h          |    2 ++
>>>    2 files changed, 3 insertions(+), 1 deletion(-)
>>>
>>> Index: linux-pm/drivers/cpuidle/governors/menu.c
>>> ===================================================================
>>> --- linux-pm.orig/drivers/cpuidle/governors/menu.c
>>> +++ linux-pm/drivers/cpuidle/governors/menu.c
>>> @@ -296,7 +296,7 @@ static int menu_select(struct cpuidle_dr
>>>    		data->needs_update = 0;
>>>    	}
>>>
>>> -	data->last_state_idx = 0;
>>> +	data->last_state_idx = CPUIDLE_DRIVER_STATE_POLL;
>>>
>>>    	/* Special case when user has set very strict latency requirement */
>>>    	if (unlikely(latency_req == 0))
>>> Index: linux-pm/include/linux/cpuidle.h
>>> ===================================================================
>>> --- linux-pm.orig/include/linux/cpuidle.h
>>> +++ linux-pm/include/linux/cpuidle.h
>>> @@ -217,8 +217,10 @@ static inline int cpuidle_register_gover
>>>
>>>    #ifdef CONFIG_ARCH_HAS_CPU_RELAX
>>>    #define CPUIDLE_DRIVER_STATE_START	1
>>> +#define CPUIDLE_DRIVER_STATE_POLL	0
>>>    #else
>>>    #define CPUIDLE_DRIVER_STATE_START	0
>>> +#define CPUIDLE_DRIVER_STATE_POLL	(-ENXIO)
>>>    #endif
>>>
>>>    #endif /* _LINUX_CPUIDLE_H */
>>
>> Hi Rafael,
>>
>> CPUIDLE_DRIVER_STATE_START is only for x86. It introduces some confusion
>> in the code.
>
> I won't disagree with that.
>
>> As only two drivers are concerned by it, wouldn't make
>> sense to add the poll state to those driver directly instead of having
>> the code hacked around ? (eg. insert the poll state in the common
>> cpuidle code).
>
> Well, what about initializing data->last_state_idx to
> (CPUIDLE_DRIVER_STATE_START - 1) in menu_select() instead of introducing the
> new symbol for the time being and getting rid of CPUIDLE_DRIVER_STATE_START
> separately?

+1


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