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

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Date:	Fri, 02 May 2014 10:47:48 +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 04/30/2014 01:16 AM, Rafael J. Wysocki wrote:
> On Tuesday, April 29, 2014 01:28:03 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>
> Subject: cpuidle / menu: Return (-1) if there are no suitable states
>
> 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 (-1) 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_START - 1;

In case of x86, CPUIDLE_DRIVER_STATE_START will be 1, so the select 
function could return 0 even this one is disabled and this is not what 
you want to happen, no ?


>   	/* Special case when user has set very strict latency requirement */
>   	if (unlikely(latency_req == 0))
>


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