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Date: Sun, 9 Sep 2012 23:46:39 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Rajagopal Venkat <rajagopal.venkat@...aro.org>
Cc: mturquette@...aro.org, myungjoo.ham@...sung.com,
kyungmin.park@...sung.com, patches@...aro.org,
linaro-dev@...ts.linaro.org, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] devfreq: core updates to support devices which can idle
On Monday, September 03, 2012, Rajagopal Venkat wrote:
> Prepare devfreq core framework to support devices which
> can idle. When device idleness is detected perhaps through
> runtime-pm, need some mechanism to suspend devfreq load
> monitoring and resume back when device is online. Present
> code continues monitoring unless device is removed from
> devfreq core.
>
> This patch introduces following design changes,
>
> - use per device work instead of global work to monitor device
> load. This enables suspend/resume of device devfreq and
> reduces monitoring code complexity.
> - decouple delayed work based load monitoring logic from core
> by introducing helpers functions to be used by governors. This
> provides flexibility for governors either to use delayed work
> based monitoring functions or to implement their own mechanism.
> - devfreq core interacts with governors via events to perform
> specific actions. These events include start/stop devfreq.
> This sets ground for adding suspend/resume events.
>
> The devfreq apis are not modified and are kept intact.
>
> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>
This one looks like a nice simplification. I wonder if everyone in the CC list
is fine with it?
One remark below.
> ---
> drivers/devfreq/devfreq.c | 376 ++++++++++--------------------
> drivers/devfreq/governor.h | 9 +
> drivers/devfreq/governor_performance.c | 16 +-
> drivers/devfreq/governor_powersave.c | 16 +-
> drivers/devfreq/governor_simpleondemand.c | 33 +++
> drivers/devfreq/governor_userspace.c | 23 +-
> include/linux/devfreq.h | 31 +--
> 7 files changed, 220 insertions(+), 284 deletions(-)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index b146d76..be524c7 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -30,17 +30,11 @@
> struct class *devfreq_class;
>
> /*
> - * devfreq_work periodically monitors every registered device.
> - * The minimum polling interval is one jiffy. The polling interval is
> - * determined by the minimum polling period among all polling devfreq
> - * devices. The resolution of polling interval is one jiffy.
> + * devfreq core provides delayed work based load monitoring helper
> + * functions. Governors can use these or can implement their own
> + * monitoring mechanism.
> */
> -static bool polling;
> static struct workqueue_struct *devfreq_wq;
> -static struct delayed_work devfreq_work;
> -
> -/* wait removing if this is to be removed */
> -static struct devfreq *wait_remove_device;
>
> /* The list of all device-devfreq */
> static LIST_HEAD(devfreq_list);
> @@ -72,6 +66,8 @@ static struct devfreq *find_device_devfreq(struct device *dev)
> return ERR_PTR(-ENODEV);
> }
>
> +/* Load monitoring helper functions for governors use */
> +
> /**
> * update_devfreq() - Reevaluate the device and configure frequency.
> * @devfreq: the devfreq instance.
> @@ -121,6 +117,90 @@ int update_devfreq(struct devfreq *devfreq)
> }
>
> /**
> + * devfreq_monitor() - Periodically poll devfreq objects.
> + * @work: the work struct used to run devfreq_monitor periodically.
> + *
> + */
> +static void devfreq_monitor(struct work_struct *work)
> +{
> + int err;
> + struct devfreq *devfreq = container_of(work,
> + struct devfreq, work.work);
> +
> + mutex_lock(&devfreq->lock);
> + err = update_devfreq(devfreq);
> + mutex_unlock(&devfreq->lock);
> + if (err)
> + dev_err(&devfreq->dev, "dvfs failed with (%d) error\n", err);
> +
> + queue_delayed_work(devfreq_wq, &devfreq->work,
> + msecs_to_jiffies(devfreq->profile->polling_ms));
> +}
> +
> +/**
> + * devfreq_monitor_start() - Start load monitoring of devfreq instance
> + * using default delayed work
> + * @devfreq: the devfreq instance.
> + *
> + * Returns 0 if monitoring started, non-zero otherwise.
> + * Note: This function is exported for governors.
> + */
> +int devfreq_monitor_start(struct devfreq *devfreq)
> +{
> + INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
> + return !queue_delayed_work(devfreq_wq, &devfreq->work,
> + msecs_to_jiffies(devfreq->profile->polling_ms));
> +}
> +
> +/**
> + * devfreq_monitor_stop() - Stop load monitoring of a devfreq instance
> + * @devfreq: the devfreq instance.
> + *
> + * Note: This function is exported for governors.
> + */
> +void devfreq_monitor_stop(struct devfreq *devfreq)
> +{
> + cancel_delayed_work_sync(&devfreq->work);
> +}
> +
> +/**
> + * devfreq_monitor_suspend() - Suspend load monitoring of a devfreq instance
> + * @devfreq: the devfreq instance.
> + *
> + * Note: This function is exported for governors.
> + */
It would be good to say in the kerneldoc comment what the idea is, because it
is not particularly clear from the code. In particular, why can't
devfreq_monitor_suspend() be the same as devfreq_monitor_stop()?
> +int devfreq_monitor_suspend(struct devfreq *devfreq)
> +{
> + int ret = -EPERM;
> +
> + if (delayed_work_pending(&devfreq->work)) {
> + cancel_delayed_work_sync(&devfreq->work);
> + ret = 0;
> + }
> +
> + return ret;
> +}
> +
> +/**
> + * devfreq_monitor_resume() - Resume load monitoring of a devfreq instance
> + * @devfreq: the devfreq instance.
> + *
> + * Returns 0 if monitoring re-started, non-zero otherwise.
> + * Note: This function is exported for governors.
It would be good to explain the idea here too.
> + */
> +int devfreq_monitor_resume(struct devfreq *devfreq)
> +{
> + int ret = -EPERM;
> +
> + if (!delayed_work_pending(&devfreq->work)) {
> + ret = !queue_delayed_work(devfreq_wq, &devfreq->work,
> + msecs_to_jiffies(devfreq->profile->polling_ms));
> + }
> +
> + return ret;
> +}
Thanks,
Rafael
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