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Message-ID: <CAKfTPtDkdom+YQieLQ=H8cG0_34g2dADYbDz7-i2iVY4JyOvsQ@mail.gmail.com>
Date: Thu, 9 Nov 2017 08:51:04 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Len Brown <lenb@...nel.org>
Cc: thomas.ilsche@...dresden.de, dsmythies@...us.net,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
jacob.jun.pan@...ux.intel.com,
linux-kernel <linux-kernel@...r.kernel.org>,
Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and
allow HW to go deep
Hi Len
On 9 November 2017 at 08:38, Len Brown <lenb@...nel.org> wrote:
> From: Len Brown <len.brown@...el.com>
>
> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
> cpuidle to shallow idle states, there is no simple mechanism
> to give the hardware permission to enter the deeptest state permitted by PM_QOS.
and by per device resume latency QoS
>
> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>
> "cpuidle.use_deepest=Y" can be set at boot-time, and
> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> n.b.
>
> Within the constraints of PM_QOS, this mechanism gives the hardware
> permission to choose the deeptest power savings and highest latency
> state available. And so choice will depend on the particular hardware.
>
> Also, if PM_QOS is not informed of latency constraints, it can't help.
> In that case, using this mechanism may result in entering high-latency
> states that impact performance.
>
> Signed-off-by: Len Brown <len.brown@...el.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 4 ++++
> drivers/cpuidle/cpuidle.c | 19 ++++++++++++++++
> include/linux/cpuidle.h | 7 ++++++
> kernel/sched/idle.c | 30 +++++++++++++++++++------
> 4 files changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 05496622b4ef..20f70de688bf 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -659,6 +659,10 @@
> cpuidle.off=1 [CPU_IDLE]
> disable the cpuidle sub-system
>
> + cpuidle.use_deepest=Y [CPU_IDLE]
> + Ignore cpuidle governor, always choose deepest
> + PM_QOS-legal CPU idle power saving state.
> +
> cpufreq.off=1 [CPU_FREQ]
> disable the cpufreq sub-system
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 484cc8909d5c..afee5aab7719 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -34,6 +34,7 @@ LIST_HEAD(cpuidle_detected_devices);
>
> static int enabled_devices;
> static int off __read_mostly;
> +static bool use_deepest __read_mostly;
> static int initialized __read_mostly;
>
> int cpuidle_disabled(void)
> @@ -116,6 +117,10 @@ void cpuidle_use_deepest_state(bool enable)
> preempt_enable();
> }
>
> +bool cpuidle_using_deepest_state(void)
> +{
> + return use_deepest;
> +}
> /**
> * cpuidle_find_deepest_state - Find the deepest available idle state.
> * @drv: cpuidle driver for the given CPU.
> @@ -127,6 +132,19 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> return find_deepest_state(drv, dev, UINT_MAX, 0, false);
> }
>
> +/**
> + * cpuidle_find_deepest_state_qos - Find the deepest available idle state.
> + * @drv: cpuidle driver for the given CPU.
> + * @dev: cpuidle device for the given CPU.
> + * Honors PM_QOS
> + */
> +int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev)
> +{
> + return find_deepest_state(drv, dev,
> + pm_qos_request(PM_QOS_CPU_DMA_LATENCY), 0, false);
You should also take into account per device latency like in menu governor:
dev_pm_qos_raw_read_value(device);
> +}
> +
> #ifdef CONFIG_SUSPEND
> static void enter_s2idle_proper(struct cpuidle_driver *drv,
> struct cpuidle_device *dev, int index)
> @@ -681,4 +699,5 @@ static int __init cpuidle_init(void)
> }
>
> module_param(off, int, 0444);
> +module_param(use_deepest, bool, 0644);
> core_initcall(cpuidle_init);
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 8f7788d23b57..e3c2c9d1898f 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -198,19 +198,26 @@ static inline struct cpuidle_device *cpuidle_get_device(void) {return NULL; }
> #ifdef CONFIG_CPU_IDLE
> extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> struct cpuidle_device *dev);
> +extern int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev);
> extern int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
> struct cpuidle_device *dev);
> extern void cpuidle_use_deepest_state(bool enable);
> +extern bool cpuidle_using_deepest_state(void);
> #else
> static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> struct cpuidle_device *dev)
> {return -ENODEV; }
> +static inline int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev)
> +{return -ENODEV; }
> static inline int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
> struct cpuidle_device *dev)
> {return -ENODEV; }
> static inline void cpuidle_use_deepest_state(bool enable)
> {
> }
> +static inline bool cpuidle_using_deepest_state(void) {return false; }
> #endif
>
> /* kernel/sched/idle.c */
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 257f4f0b4532..6c7348ae28ec 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -167,17 +167,33 @@ static void cpuidle_idle_call(void)
> * until a proper wakeup interrupt happens.
> */
>
> - if (idle_should_enter_s2idle() || dev->use_deepest_state) {
> - if (idle_should_enter_s2idle()) {
> - entered_state = cpuidle_enter_s2idle(drv, dev);
> - if (entered_state > 0) {
> - local_irq_enable();
> - goto exit_idle;
> - }
> + if (idle_should_enter_s2idle()) {
> + entered_state = cpuidle_enter_s2idle(drv, dev);
> + if (entered_state > 0) {
> + local_irq_enable();
> + goto exit_idle;
> }
> + }
>
> + /*
> + * cpuidle_dev->user_deepest_state is per-device, and thus per-CPU.
> + * it is used to force power-savings, and thus does not obey PM_QOS.
> + */
> +
> + if (dev->use_deepest_state) {
> next_state = cpuidle_find_deepest_state(drv, dev);
> call_cpuidle(drv, dev, next_state);
> + }
> +
> + /*
> + * cpuidle_using_deepest_state() is system-wide, applying to all CPUs.
> + * When activated, Linux gives the hardware permission to go as deep
> + * as PM_QOS allows.
> + */
> +
> + else if (cpuidle_using_deepest_state()) {
> + next_state = cpuidle_find_deepest_state_qos(drv, dev);
> + call_cpuidle(drv, dev, next_state);
> } else {
> /*
> * Ask the cpuidle framework to choose a convenient idle state.
> --
> 2.14.0-rc0
>
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