Re: [PATCH] drm/panfrost: Add governor data with pre-defined thresholds

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 21/01/2021 18:04, Lukasz Luba wrote:
> The simple_ondemand devfreq governor uses two thresholds to decide about
> the frequency change: upthreshold, downdifferential. These two tunable
> change the behavior of the governor decision, e.g. how fast to increase
> the frequency or how rapidly limit the frequency. This patch adds needed
> governor data with thresholds values gathered experimentally in different
> workloads.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
> Hi all,
> 
> This patch aims to improve the panfrost performance in various workloads,
> (benchmarks, games). The simple_ondemand devfreq governor supports
> tunables to tweak the behaviour of the internal algorithm. The default
> values for these two thresholds (90 and 5) do not work well with panfrost.
> These new settings should provide good performance, short latency for
> rising the frequency due to rapid workload change and decent freq slow
> down when the load is decaying. Based on frequency change statistics,
> gathered during experiments, all frequencies are used, depending on
> the load. This provides some power savings (statistically). The highest
> frequency is also used when needed.
> 
> Example glmark2 results:
> 1. freq fixed to max: 153
> 2. these new thresholds values (w/ patch): 151
> 3. default governor values (w/o patch): 114
> 
> In future the devfreq framework would expose via sysfs these two
> tunables, so they can be adjusted by the middleware based on currently
> running workload (game, desktop, web browser, etc). These new values
> should be good enough, though.
> 
> Regards,
> Lukasz Luba
> 
>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 10 +++++++++-
>  drivers/gpu/drm/panfrost/panfrost_devfreq.h |  2 ++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index 56b3f5935703..7c5ffc81dce1 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -130,8 +130,16 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>  	panfrost_devfreq_profile.initial_freq = cur_freq;
>  	dev_pm_opp_put(opp);
>  
> +	/*
> +	 * Setup default thresholds for the simple_ondemand governor.
> +	 * The values are chosen based on experiments.
> +	 */
> +	pfdevfreq->gov_data.upthreshold = 45;
> +	pfdevfreq->gov_data.downdifferential = 5;
> +
>  	devfreq = devm_devfreq_add_device(dev, &panfrost_devfreq_profile,
> -					  DEVFREQ_GOV_SIMPLE_ONDEMAND, NULL);
> +					  DEVFREQ_GOV_SIMPLE_ONDEMAND,
> +					  &pfdevfreq->gov_data);
>  	if (IS_ERR(devfreq)) {
>  		DRM_DEV_ERROR(dev, "Couldn't initialize GPU devfreq\n");
>  		ret = PTR_ERR(devfreq);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.h b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
> index db6ea48e21f9..1e2a4de941aa 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
> @@ -4,6 +4,7 @@
>  #ifndef __PANFROST_DEVFREQ_H__
>  #define __PANFROST_DEVFREQ_H__
>  
> +#include <linux/devfreq.h>
>  #include <linux/spinlock.h>
>  #include <linux/ktime.h>
>  
> @@ -17,6 +18,7 @@ struct panfrost_devfreq {
>  	struct devfreq *devfreq;
>  	struct opp_table *regulators_opp_table;
>  	struct thermal_cooling_device *cooling;
> +	struct devfreq_simple_ondemand_data gov_data;
>  	bool opp_of_table_added;
>  
>  	ktime_t busy_time;

I think it is simpler to do:

+static struct devfreq_simple_ondemand_data panfrost_ondemand_data = {
+       .upthreshold = 45,
+       .downdifferential = 5,
+};

[ ... ]

       devfreq = devm_devfreq_add_device(dev, &panfrost_devfreq_profile,
-                                         DEVFREQ_GOV_SIMPLE_ONDEMAND,
NULL);
+                                         DEVFREQ_GOV_SIMPLE_ONDEMAND,
+                                         &panfrost_ondemand_data);


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