linux-kernel - Re: [PATCH v2 2/3] cpu: expose pm_qos_resume

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Date:   Tue, 17 Jan 2017 11:23:30 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Alex Shi <alex.shi@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        vincent.guittot@...aro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v2 2/3] cpu: expose pm_qos_resume_latency for each cpu

On Thu, Jan 12, 2017 at 09:27:03PM +0800, Alex Shi wrote:
> The cpu-dma PM QoS constraint impacts all the cpus in the system. There
> is no way to let the user to choose a PM QoS constraint per cpu.
> 
> The following patch exposes to the userspace a per cpu based sysfs file
> in order to let the userspace to change the value of the PM QoS latency
> constraint.
> 
> This change is inoperative in its form and the cpuidle governors have to
> take into account the per cpu latency constraint in addition to the
> global cpu-dma latency constraint in order to operate properly.
> 
> BTW
> The pm_qos_resume_latency usage defined in
> Documentation/ABI/testing/sysfs-devices-power
> The /sys/devices/.../power/pm_qos_resume_latency_us attribute
> contains the PM QoS resume latency limit for the given device,
> which is the maximum allowed time it can take to resume the
> device, after it has been suspended at run time, from a resume
> request to the moment the device will be ready to process I/O,
> in microseconds.  If it is equal to 0, however, this means that
> the PM QoS resume latency may be arbitrary.
> 
> Signed-off-by: Alex Shi <alex.shi@...aro.org>
> To: linux-kernel@...r.kernel.org
> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-pm@...r.kernel.org
> Cc: Ulf Hansson <ulf.hansson@...aro.org>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> ---
>  drivers/base/cpu.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 4c28e1a..2c3b359 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -17,6 +17,7 @@
>  #include <linux/of.h>
>  #include <linux/cpufeature.h>
>  #include <linux/tick.h>
> +#include <linux/pm_qos.h>
>  
>  #include "base.h"
>  
> @@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
>  
>  	per_cpu(cpu_sys_devices, num) = &cpu->dev;
>  	register_cpu_under_node(num, cpu_to_node(num));
> +	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);

This patch should be submitted as the last patch in the latencies constraint
changes patchset IMO. It is pointless to provide an interface before a
feature which is still under discussion.


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