linux-kernel - Re: [PATCH V2 3/5] cpuidle: idle: menu: Don't reflect when a state selection failed

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Date:	Wed, 29 Oct 2014 22:11 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Kevin Hilman <khilman@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Preeti Murthy <preeti.lkml@...il.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	patches@...aro.org, Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH V2 3/5] cpuidle: idle: menu: Don't reflect when a state selection failed

On Wednesday, October 29, 2014 09:54:43 AM Kevin Hilman wrote:
> Daniel Lezcano <daniel.lezcano@...aro.org> writes:
> 
> > On 10/28/2014 08:01 AM, Preeti Murthy wrote:
> >> On Thu, Oct 23, 2014 at 2:31 PM, Daniel Lezcano
> >> <daniel.lezcano@...aro.org> wrote:
> >>> In the current code, the check to reflect or not the outcoming state is done
> >>> against the idle state which has been chosen and its value.
> >>>
> >>> Instead of doing a check in each of the reflect functions, just don't call reflect
> >>> if something went wrong in the idle path.
> >>>
> >>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> >>> Acked-by: Nicolas Pitre <nico@...aro.org>
> >>> ---
> >>>   drivers/cpuidle/governors/ladder.c | 3 +--
> >>>   drivers/cpuidle/governors/menu.c   | 4 +---
> >>>   kernel/sched/idle.c                | 3 ++-
> >>>   3 files changed, 4 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
> >>> index fb396d6..c0b36a8 100644
> >>> --- a/drivers/cpuidle/governors/ladder.c
> >>> +++ b/drivers/cpuidle/governors/ladder.c
> >>> @@ -165,8 +165,7 @@ static int ladder_enable_device(struct cpuidle_driver *drv,
> >>>   static void ladder_reflect(struct cpuidle_device *dev, int index)
> >>>   {
> >>>          struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
> >>> -       if (index > 0)
> >>> -               ldev->last_state_idx = index;
> >>> +       ldev->last_state_idx = index;
> >>>   }
> >>>
> >>>   static struct cpuidle_governor ladder_governor = {
> >>> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> >>> index a17515f..3907301 100644
> >>> --- a/drivers/cpuidle/governors/menu.c
> >>> +++ b/drivers/cpuidle/governors/menu.c
> >>> @@ -365,9 +365,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> >>>   static void menu_reflect(struct cpuidle_device *dev, int index)
> >>>   {
> >>>          struct menu_device *data = &__get_cpu_var(menu_devices);
> >>> -       data->last_state_idx = index;
> >>> -       if (index >= 0)
> >>> -               data->needs_update = 1;
> >>> +       data->needs_update = 1;
> >>
> >> Why is the last_state_idx not getting updated ?
> >
> > Oups, right. This is missing.
> >
> > Thanks for pointing this out.
> >
> > By the way, I don't think a back end driver is changing the selected
> > state currently and I am not sure this is desirable since we want to
> > trust the state we are going (as a best effort). 
> 
> FYI, the OMAP3 backend driver can does not always obey the selected
> state, and will return a different state than the one requested.

The ACPI driver can do that as well.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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