linux-kernel - Re: [PATCH v2] cpuidle: ladder: Add per CPU PM QoS resume latency support

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Date:   Fri, 27 Oct 2017 09:59:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     ramesh.thomas@...el.com
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Alex Shi <alex.shi@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2] cpuidle: ladder: Add per CPU PM QoS resume latency support

On Fri, Oct 27, 2017 at 4:01 AM, Ramesh Thomas <ramesh.thomas@...el.com> wrote:
> Individual CPUs may have special requirements to not enter
> deep idle states. For example, a CPU running real time
> applications would not want to enter deep idle states to
> avoid latency impacts. At the same time other CPUs that
> do not have such a requirement could allow deep idle
> states to save power.
>
> This was already implemented in the menu governor.
> Implementing similar changes in the ladder governor which
> gets selected when CONFIG_NO_HZ and CONFIG_NO_HZ_IDLE are not
> set. Refer following commits for the menu governor changes.
>
> commit 9908859acaa9 ("cpuidle/menu: add per CPU PM QoS resume
> latency consideration")
> commit 6dbf5cea05a7 ("cpuidle: menu: Avoid taking spinlock for
> accessing QoS values")
>
> Signed-off-by: Ramesh Thomas <ramesh.thomas@...el.com>
> ---
>
> v2:
>   - use PM_QOS_RESUME_LATENCY_NO_CONSTRAINT for "no constraint" value
>   Should be applied over https://patchwork.kernel.org/patch/10024157/
>
>  drivers/cpuidle/governors/ladder.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
> index ce1a2ff..1ad8745 100644
> --- a/drivers/cpuidle/governors/ladder.c
> +++ b/drivers/cpuidle/governors/ladder.c
> @@ -17,6 +17,7 @@
>  #include <linux/pm_qos.h>
>  #include <linux/jiffies.h>
>  #include <linux/tick.h>
> +#include <linux/cpu.h>
>
>  #include <asm/io.h>
>  #include <linux/uaccess.h>
> @@ -67,10 +68,16 @@ static int ladder_select_state(struct cpuidle_driver *drv,
>                                 struct cpuidle_device *dev)
>  {
>         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
> +       struct device *device = get_cpu_device(dev->cpu);
>         struct ladder_device_state *last_state;
>         int last_residency, last_idx = ldev->last_state_idx;
>         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
>         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
> +       int resume_latency = dev_pm_qos_raw_read_value(device);
> +
> +       if (resume_latency < latency_req &&
> +           resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> +               latency_req = resume_latency;
>
>         /* Special case when user has set very strict latency requirement */
>         if (unlikely(latency_req == 0)) {
> --
> 2.7.4
>

Looks good to me.

I'll queue it up if nobody objects.

Thanks,
Rafael