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 01:16:45 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
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 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>
> > >
> > > 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?

Updated patch is appended for completness.

Thanks!

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

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