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

From: Rafael J. Wysocki
Date: Tue Apr 29 2014 - 19:00:26 EST


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@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxx>
> > > ---
> > > 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@xxxxxxxxx>
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@xxxxxxxxx>
---
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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