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Message-ID: <20200114190743.GK89495@google.com>
Date: Tue, 14 Jan 2020 11:07:43 -0800
From: Matthias Kaehlcke <mka@...omium.org>
To: Leonard Crestez <leonard.crestez@....com>
Cc: Chanwoo Choi <cw00.choi@...sung.com>,
MyungJoo Ham <myungjoo.ham@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Zhang Rui <rui.zhang@...el.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Amit Kucheria <amit.kucheria@...durent.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
"Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 1/2] thermal: devfreq_cooling: Use PM QoS to set
frequency limits
On Tue, Jan 14, 2020 at 04:08:38PM +0000, Leonard Crestez wrote:
> On 10.01.2020 19:49, Matthias Kaehlcke wrote:
> > Now that devfreq supports limiting the frequency range of a device
> > through PM QoS make use of it instead of disabling OPPs that should
> > not be used.
> >
> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > ---
>
> It is not obvious but this changes behavior when min max requests
> conflict (min > max): with PM QoS a MIN_FREQUENCY request takes
> precedence but if higher OPPs are disabled then this will override
> MIN_FREQUENCY.
Thanks for pointing this out.
> There are very few users of this functionality so I don't think there
> are any systems that depend on this behaving one way or the other but
> perhaps it should be mentioned in commit message?
Sounds good, I'll add a note.
> As far as I can tell the only user of devfreq_cooling in upstream is
> drivers/gpu/drm/panfrost?
Indeed, apparently GPUs are the primary devfreq device used for cooling,
and unfortunately most GPU drivers are not in upstream.
> > drivers/thermal/devfreq_cooling.c | 66 ++++++++++---------------------
> > 1 file changed, 20 insertions(+), 46 deletions(-)
> >
> > diff --git a/drivers/thermal/devfreq_cooling.c b/drivers/thermal/devfreq_cooling.c
> > index ef59256887ff..3a63603afcf2 100644
> > --- a/drivers/thermal/devfreq_cooling.c
> > +++ b/drivers/thermal/devfreq_cooling.c
> > @@ -24,11 +24,13 @@
> > #include <linux/idr.h>
> > #include <linux/slab.h>
> > #include <linux/pm_opp.h>
> > +#include <linux/pm_qos.h>
> > #include <linux/thermal.h>
> >
> > #include <trace/events/thermal.h>
> >
> > -#define SCALE_ERROR_MITIGATION 100
> > +#define HZ_PER_KHZ 1000
> > +#define SCALE_ERROR_MITIGATION 100
> >
> > static DEFINE_IDA(devfreq_ida);
> >
> > @@ -65,49 +67,9 @@ struct devfreq_cooling_device {
> > struct devfreq_cooling_power *power_ops;
> > u32 res_util;
> > int capped_state;
> > + struct dev_pm_qos_request req_max_freq;
> > };
> >
> > -/**
> > - * partition_enable_opps() - disable all opps above a given state
> > - * @dfc: Pointer to devfreq we are operating on
> > - * @cdev_state: cooling device state we're setting
> > - *
> > - * Go through the OPPs of the device, enabling all OPPs until
> > - * @cdev_state and disabling those frequencies above it.
> > - */
> > -static int partition_enable_opps(struct devfreq_cooling_device *dfc,
> > - unsigned long cdev_state)
> > -{
> > - int i;
> > - struct device *dev = dfc->devfreq->dev.parent;
> > -
> > - for (i = 0; i < dfc->freq_table_size; i++) {
> > - struct dev_pm_opp *opp;
> > - int ret = 0;
> > - unsigned int freq = dfc->freq_table[i];
> > - bool want_enable = i >= cdev_state ? true : false;
> > -
> > - opp = dev_pm_opp_find_freq_exact(dev, freq, !want_enable);
> > -
> > - if (PTR_ERR(opp) == -ERANGE)
> > - continue;
> > - else if (IS_ERR(opp))
> > - return PTR_ERR(opp);
> > -
> > - dev_pm_opp_put(opp);
> > -
> > - if (want_enable)
> > - ret = dev_pm_opp_enable(dev, freq);
> > - else
> > - ret = dev_pm_opp_disable(dev, freq);
> > -
> > - if (ret)
> > - return ret;
> > - }
> > -
> > - return 0;
> > -}
> > -
> > static int devfreq_cooling_get_max_state(struct thermal_cooling_device *cdev,
> > unsigned long *state)
> > {
> > @@ -134,7 +96,7 @@ static int devfreq_cooling_set_cur_state(struct thermal_cooling_device *cdev,
> > struct devfreq_cooling_device *dfc = cdev->devdata;
> > struct devfreq *df = dfc->devfreq;
> > struct device *dev = df->dev.parent;
> > - int ret;
> > + unsigned long freq;
> >
> > if (state == dfc->cooling_state)
> > return 0;
> > @@ -144,9 +106,10 @@ static int devfreq_cooling_set_cur_state(struct thermal_cooling_device *cdev,
> > if (state >= dfc->freq_table_size)
> > return -EINVAL;
> >
> > - ret = partition_enable_opps(dfc, state);
> > - if (ret)
> > - return ret;
> > + freq = dfc->freq_table[state];
> > +
> > + dev_pm_qos_update_request(&dfc->req_max_freq,
> > + DIV_ROUND_UP(freq, HZ_PER_KHZ));
> >
> > dfc->cooling_state = state;
> >
> > @@ -529,6 +492,12 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
> > if (err)
> > goto free_dfc;
> >
> > + err = dev_pm_qos_add_request(df->dev.parent, &dfc->req_max_freq,
> > + DEV_PM_QOS_MAX_FREQUENCY,
> > + PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
> > + if (err < 0)
> > + goto remove_qos_req;
> > +
> > err = ida_simple_get(&devfreq_ida, 0, 0, GFP_KERNEL);
> > if (err < 0)
> > goto free_tables;
> > @@ -552,6 +521,10 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
> >
> > release_ida:
> > ida_simple_remove(&devfreq_ida, dfc->id);
> > +
> > +remove_qos_req:
> > + dev_pm_qos_remove_request(&dfc->req_max_freq); > +
>
> A quirk of the dev_pm_qos API is that dev_pm_qos_remove_request prints a
> WARN splat if !dev_pm_qos_request_active and this can true on
> dev_pm_qos_add_request error.
>
> I dealt with this by checking dev_pm_qos_request_active explicitly but
> perhaps dev_pm_qos API could be changed? In general "free/release"
> functions shouldn't complain if there's nothing to do.
I think we should be good here if we jump to 'free_tables' if
_add_request() fails, as requested by Chanwoo. Then _remove_request() is
only called when _add_request() was successful.
> > free_tables:
> > kfree(dfc->power_table);
> > kfree(dfc->freq_table);
> > @@ -600,6 +573,7 @@ void devfreq_cooling_unregister(struct thermal_cooling_device *cdev)
> >
> > thermal_cooling_device_unregister(dfc->cdev);
> > ida_simple_remove(&devfreq_ida, dfc->id);
> > + dev_pm_qos_remove_request(&dfc->req_max_freq);
> > kfree(dfc->power_table);
> > kfree(dfc->freq_table);
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