* Peter Zijlstra <a.p.zijls...@chello.nl> [2009-08-27 14:53:27]:
> On Thu, 2009-08-27 at 17:23 +0530, Arun R Bharadwaj wrote:
> > * Arun R Bharadwaj <a...@linux.vnet.ibm.com> [2009-08-27 17:19:08]:
> >
> > Cpuidle infrastructure assumes pm_idle as the default idle routine.
> > But, ppc_md.power_save is the default idle callback in case of pSeries.
> >
> > So, create a more generic, architecture independent cpuidle_pm_idle
> > function pointer in driver/cpuidle/cpuidle.c and allow the idle routines
> > of architectures to be set to cpuidle_pm_idle.
> >
> > Signed-off-by: Arun R Bharadwaj <a...@linux.vnet.ibm.com>
> > ---
> > drivers/cpuidle/cpuidle.c | 12 +++++++-----
> > include/linux/cpuidle.h | 7 +++++++
> > 2 files changed, 14 insertions(+), 5 deletions(-)
> >
> > Index: linux.trees.git/drivers/cpuidle/cpuidle.c
> > ===================================================================
> > --- linux.trees.git.orig/drivers/cpuidle/cpuidle.c
> > +++ linux.trees.git/drivers/cpuidle/cpuidle.c
> > @@ -25,6 +25,7 @@ DEFINE_PER_CPU(struct cpuidle_device *,
> > DEFINE_MUTEX(cpuidle_lock);
> > LIST_HEAD(cpuidle_detected_devices);
> > static void (*pm_idle_old)(void);
> > +void (*cpuidle_pm_idle)(void);
> >
> > static int enabled_devices;
> >
> > @@ -98,10 +99,10 @@ static void cpuidle_idle_call(void)
> > */
> > void cpuidle_install_idle_handler(void)
> > {
> > - if (enabled_devices && (pm_idle != cpuidle_idle_call)) {
> > + if (enabled_devices && (cpuidle_pm_idle != cpuidle_idle_call)) {
> > /* Make sure all changes finished before we switch to new idle
> > */
> > smp_wmb();
> > - pm_idle = cpuidle_idle_call;
> > + cpuidle_pm_idle = cpuidle_idle_call;
> > }
> > }
> >
> > @@ -110,8 +111,9 @@ void cpuidle_install_idle_handler(void)
> > */
> > void cpuidle_uninstall_idle_handler(void)
> > {
> > - if (enabled_devices && pm_idle_old && (pm_idle != pm_idle_old)) {
> > - pm_idle = pm_idle_old;
> > + if (enabled_devices && pm_idle_old &&
> > + (cpuidle_pm_idle != pm_idle_old)) {
> > + cpuidle_pm_idle = pm_idle_old;
> > cpuidle_kick_cpus();
> > }
> > }
> > @@ -382,7 +384,7 @@ static int __init cpuidle_init(void)
> > {
> > int ret;
> >
> > - pm_idle_old = pm_idle;
> > + pm_idle_old = cpuidle_pm_idle;
> >
> > ret = cpuidle_add_class_sysfs(&cpu_sysdev_class);
> > if (ret)
> > Index: linux.trees.git/include/linux/cpuidle.h
> > ===================================================================
> > --- linux.trees.git.orig/include/linux/cpuidle.h
> > +++ linux.trees.git/include/linux/cpuidle.h
> > @@ -188,4 +188,11 @@ static inline void cpuidle_unregister_go
> > #define CPUIDLE_DRIVER_STATE_START 0
> > #endif
> >
> > +/*
> > + * Idle callback used by cpuidle to call the cpuidle_idle_call().
> > + * Platform drivers can use this to register to cpuidle's idle loop.
> > + */
> > +
> > +extern void (*cpuidle_pm_idle)(void);
> > +
> > #endif /* _LINUX_CPUIDLE_H */
>
>
> I'm not quite seeing how this makes anything any better. Not we have 3
> function pointers, where 1 should suffice.
>
Not really. We already do have pm_idle in case of x86 and
ppc_md.power_save in case of POWER. So here I'm only introducing
cpuidle_pm_idle which can be used by doing a
ppc_md.power_save = cpuidle_pm_idle;
> /me wonders what's wrong with something like:
>
> struct idle_func_desc {
> int power;
> int latency;
> void (*idle)(void);
> struct list_head list;
> };
>
> static void spin_idle(void)
> {
> for (;;)
> cpu_relax();
> }
>
> static idle_func_desc default_idle_func = {
> power = 0, /* doesn't safe any power */
> latency = INT_MAX, /* has max latency */
> idle = spin_idle,
> list = INIT_LIST_HEAD(default_idle_func.list),
> };
>
> void (*idle_func)(void);
> static struct list_head idle_func_list;
>
> static void pick_idle_func(void)
> {
> struct idle_func_desc *desc, *idle = &default_idle_desc;
>
> list_for_each_entry(desc, &idle_func_list, list) {
> if (desc->power < idle->power)
> continue;
> if (desc->latency > target_latency);
> continue;
> idle = desc;
> }
>
> pm_idle = idle->idle;
> }
>
This only does the job of picking the right idle loop for current
latency and power requirement. This is already done in ladder/menu
governors under the routines menu_select()/ladder_select().
I'm not sure whats the purpose of it here.
Here we are only concerned about the main idle loop, which is
pm_idle/ppc_md.power_save. After setting the main idle loop to
cpuidle_pm_idle, that would call cpuidle_idle_call() which would do
the job of picking the right low level idle loop based on latency and
other requirements.
> void register_idle_func(struct idle_func_desc *desc)
> {
> WARN_ON_ONCE(!list_empty(&desc->list));
>
> list_add_tail(&idle_func_list, &desc->list);
> pick_idle_func();
> }
>
> void unregister_idle_func(struct idle_func_desc *desc)
> {
> WARN_ON_ONCE(list_empty(&desc->list));
>
> list_del_init(&desc->list);
> if (idle_func == desc->idle)
> pick_idle_func();
> }
>
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