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Date: Mon, 12 Nov 2012 13:09:40 -0800
From: Julius Werner <jwerner@...omium.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: linux-pm@...r.kernel.org, khilman@...com, len.brown@...el.com,
Trinabh Gupta <g.trinabh@...il.com>,
deepthi@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
rjw@...k.pl, akpm@...ux-foundation.org,
Sameer Nanda <snanda@...omium.org>,
Lists Linaro-dev <linaro-dev@...ts.linaro.org>
Subject: Re: [RFC] cpuidle - remove the power_specified field in the driver
Thanks for moving this along, Daniel. I think this is the right
approach... the cpuidle driver shouldn't be more complex than
necessary.
Note that you are starting your loop too high in cpuidle_play_dead...
states[state_count] is not an actual state anymore, it should start at
state_count - 1. Also, I think you can go ahead and do the same
last-to-first loop transformation with immediate return in the menu
governor, for an extra tiny bit of performance.
On Mon, Nov 12, 2012 at 12:26 PM, Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
> This patch follows the discussion about reinitializing the power usage
> when a C-state is added/removed.
>
> https://lkml.org/lkml/2012/10/16/518
>
> We realized the power usage field is never filled and when it is
> filled for tegra, the power_specified flag is not set making all these
> values to be resetted when the driver is initialized with the set_power_state
> function.
>
> Julius and I feel this is over-engineered and the power_specified
> flag could be simply removed and continue assuming the states are
> backward sorted.
>
> The menu governor select function is simplified as the power is ordered.
> Actually the condition is always true with the current code.
>
> The cpuidle_play_dead function is also simplified by doing a reverse lookup
> on the array.
>
> The set_power_states function is removed as it does no make sense anymore.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
> drivers/cpuidle/cpuidle.c | 17 ++++-------------
> drivers/cpuidle/driver.c | 25 -------------------------
> drivers/cpuidle/governors/menu.c | 8 ++------
> include/linux/cpuidle.h | 2 +-
> 4 files changed, 7 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 711dd83..f983262 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -69,24 +69,15 @@ int cpuidle_play_dead(void)
> {
> struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
> struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> - int i, dead_state = -1;
> - int power_usage = -1;
> + int i;
>
> if (!drv)
> return -ENODEV;
>
> /* Find lowest-power state that supports long-term idle */
> - for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
> - struct cpuidle_state *s = &drv->states[i];
> -
> - if (s->power_usage < power_usage && s->enter_dead) {
> - power_usage = s->power_usage;
> - dead_state = i;
> - }
> - }
> -
> - if (dead_state != -1)
> - return drv->states[dead_state].enter_dead(dev, dead_state);
> + for (i = drv->state_count; i >= CPUIDLE_DRIVER_STATE_START; i--)
> + if (drv->states[i].play_dead)
> + return drv->states[i].enter_dead(dev, i);
>
> return -ENODEV;
> }
> diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> index 3af841f..bb045f1 100644
> --- a/drivers/cpuidle/driver.c
> +++ b/drivers/cpuidle/driver.c
> @@ -19,34 +19,9 @@ DEFINE_SPINLOCK(cpuidle_driver_lock);
> static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu);
> static struct cpuidle_driver * __cpuidle_get_cpu_driver(int cpu);
>
> -static void set_power_states(struct cpuidle_driver *drv)
> -{
> - int i;
> -
> - /*
> - * cpuidle driver should set the drv->power_specified bit
> - * before registering if the driver provides
> - * power_usage numbers.
> - *
> - * If power_specified is not set,
> - * we fill in power_usage with decreasing values as the
> - * cpuidle code has an implicit assumption that state Cn
> - * uses less power than C(n-1).
> - *
> - * With CONFIG_ARCH_HAS_CPU_RELAX, C0 is already assigned
> - * an power value of -1. So we use -2, -3, etc, for other
> - * c-states.
> - */
> - for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++)
> - drv->states[i].power_usage = -1 - i;
> -}
> -
> static void __cpuidle_driver_init(struct cpuidle_driver *drv)
> {
> drv->refcnt = 0;
> -
> - if (!drv->power_specified)
> - set_power_states(drv);
> }
>
> static int __cpuidle_register_driver(struct cpuidle_driver *drv, int cpu)
> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> index 2efee27..14eb11f 100644
> --- a/drivers/cpuidle/governors/menu.c
> +++ b/drivers/cpuidle/governors/menu.c
> @@ -312,7 +312,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> {
> struct menu_device *data = &__get_cpu_var(menu_devices);
> int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
> - int power_usage = -1;
> int i;
> int multiplier;
> struct timespec t;
> @@ -383,11 +382,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> if (s->exit_latency * multiplier > data->predicted_us)
> continue;
>
> - if (s->power_usage < power_usage) {
> - power_usage = s->power_usage;
> - data->last_state_idx = i;
> - data->exit_us = s->exit_latency;
> - }
> + data->last_state_idx = i;
> + data->exit_us = s->exit_latency;
> }
>
> /* not deepest C-state chosen for low predicted residency */
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 3711b34..24cd103 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -126,9 +126,9 @@ struct cpuidle_driver {
> struct module *owner;
> int refcnt;
>
> - unsigned int power_specified:1;
> /* set to 1 to use the core cpuidle time keeping (for all states). */
> unsigned int en_core_tk_irqen:1;
> + /* states array must be ordered in decreasing power consumption */
> struct cpuidle_state states[CPUIDLE_STATE_MAX];
> int state_count;
> int safe_state_index;
> --
> 1.7.5.4
>
--
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