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From: Douglas Raillard <douglas.raillard@arm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	mingo@redhat.com, peterz@infradead.org, quentin.perret@arm.com,
	dietmar.eggemann@arm.com, rjw@rjwysocki.net,
	Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq()
Date: Thu, 16 May 2019 14:06:08 +0100
Message-ID: <046bfab7-bf28-bbfe-2bff-09881d537fb1@arm.com> (raw)
In-Reply-To: <20190516124200.opxczohjelhvrzmo@e110439-lin>

Hi Patrick,

On 5/16/19 1:42 PM, Patrick Bellasi wrote:
> On 08-May 18:42, douglas.raillard@arm.com wrote:
>> From: Douglas RAILLARD <douglas.raillard@arm.com>
>>
>> em_pd_get_higher_freq() returns a frequency greater or equal to the
>> provided one while taking into account a given cost margin. It also
>> skips inefficient OPPs that have a higher cost than another one with a
>> higher frequency.
> 
> It's worth to add a small description and definition of what we mean by
> "OPP efficiency". Despite being just an RFC, it could help to better
> understand what we are after.

Right, here efficiency=capacity/power.

> 
> [...]
> 
>> +/** + * em_pd_get_higher_freq() - Get the highest frequency that
>> does not exceed the
>> + * given cost margin compared to min_freq
>> + * @pd		: performance domain for which this must be done
>> + * @min_freq	: minimum frequency to return
>> + * @cost_margin	: allowed margin compared to min_freq, as a per-1024 value.
>                                                                      ^^^^^^^^
> here...
> 
>> + *
>> + * Return: the chosen frequency, guaranteed to be at least as high as min_freq.
>> + */
>> +static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd,
>> +	unsigned long min_freq, unsigned long cost_margin)
>> +{
>> +	unsigned long max_cost = 0;
>> +	struct em_cap_state *cs;
>> +	int i;
>> +
>> +	if (!pd)
>> +		return min_freq;
>> +
>> +	/* Compute the maximum allowed cost */
>> +	for (i = 0; i < pd->nr_cap_states; i++) {
>> +		cs = &pd->table[i];
>> +		if (cs->frequency >= min_freq) {
>> +			max_cost = cs->cost + (cs->cost * cost_margin) / 1024;
>                                                                           ^^^^
> ... end here we should probably better use SCHED_CAPACITY_SCALE
> instead of hard-coding in values, isn't it?

"cs->cost*cost_margin/1024" is not a capacity, it's a cost as defined here:
https://elixir.bootlin.com/linux/latest/source/include/linux/energy_model.h#L17

Actually, it's in milliwatts, but it's not better the better way to look at
it to understand it IMHO.

The margin is expressed as a "per-1024" value just like we use percents'
in everyday life, so it has no unit. If we want to avoid hard-coded values
here, I can introduce an ENERGY_COST_MARGIN_SCALE macro.

>> +			break;
>> +		}
>> +	}
>> +
> 
> [...]
> 
> Best,
> Patrick

Thanks,
Douglas

From: Douglas Raillard <douglas.raillard@arm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	mingo@redhat.com, peterz@infradead.org, quentin.perret@arm.com,
	dietmar.eggemann@arm.com, rjw@rjwysocki.net,
	Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq()
Date: Thu, 16 May 2019 14:06:08 +0100
Message-ID: <046bfab7-bf28-bbfe-2bff-09881d537fb1@arm.com> (raw)
Message-ID: <20190516130608.yGeCuFC3T9i2BNlpuLV9-grUHaZOnKc8Sv1TIyKaGUQ@z> (raw)
In-Reply-To: <20190516124200.opxczohjelhvrzmo@e110439-lin>

Hi Patrick,

On 5/16/19 1:42 PM, Patrick Bellasi wrote:
> On 08-May 18:42, douglas.raillard@arm.com wrote:
>> From: Douglas RAILLARD <douglas.raillard@arm.com>
>>
>> em_pd_get_higher_freq() returns a frequency greater or equal to the
>> provided one while taking into account a given cost margin. It also
>> skips inefficient OPPs that have a higher cost than another one with a
>> higher frequency.
> 
> It's worth to add a small description and definition of what we mean by
> "OPP efficiency". Despite being just an RFC, it could help to better
> understand what we are after.

Right, here efficiency=capacity/power.

> 
> [...]
> 
>> +/** + * em_pd_get_higher_freq() - Get the highest frequency that
>> does not exceed the
>> + * given cost margin compared to min_freq
>> + * @pd		: performance domain for which this must be done
>> + * @min_freq	: minimum frequency to return
>> + * @cost_margin	: allowed margin compared to min_freq, as a per-1024 value.
>                                                                      ^^^^^^^^
> here...
> 
>> + *
>> + * Return: the chosen frequency, guaranteed to be at least as high as min_freq.
>> + */
>> +static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd,
>> +	unsigned long min_freq, unsigned long cost_margin)
>> +{
>> +	unsigned long max_cost = 0;
>> +	struct em_cap_state *cs;
>> +	int i;
>> +
>> +	if (!pd)
>> +		return min_freq;
>> +
>> +	/* Compute the maximum allowed cost */
>> +	for (i = 0; i < pd->nr_cap_states; i++) {
>> +		cs = &pd->table[i];
>> +		if (cs->frequency >= min_freq) {
>> +			max_cost = cs->cost + (cs->cost * cost_margin) / 1024;
>                                                                           ^^^^
> ... end here we should probably better use SCHED_CAPACITY_SCALE
> instead of hard-coding in values, isn't it?

"cs->cost*cost_margin/1024" is not a capacity, it's a cost as defined here:
https://elixir.bootlin.com/linux/latest/source/include/linux/energy_model.h#L17

Actually, it's in milliwatts, but it's not better the better way to look at
it to understand it IMHO.

The margin is expressed as a "per-1024" value just like we use percents'
in everyday life, so it has no unit. If we want to avoid hard-coded values
here, I can introduce an ENERGY_COST_MARGIN_SCALE macro.

>> +			break;
>> +		}
>> +	}
>> +
> 
> [...]
> 
> Best,
> Patrick

Thanks,
Douglas

  parent reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08 17:42 [RFC PATCH 0/7] sched/cpufreq: Make schedutil energy aware douglas.raillard
2019-05-08 17:42 ` douglas.raillard
2019-05-08 17:42 ` [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq() douglas.raillard
2019-05-08 17:42   ` douglas.raillard
2019-05-16 12:42   ` Patrick Bellasi
2019-05-16 12:42     ` Patrick Bellasi
2019-05-16 13:01     ` Quentin Perret
2019-05-16 13:01       ` Quentin Perret
2019-05-16 13:22       ` Patrick Bellasi
2019-05-16 13:22         ` Patrick Bellasi
2019-06-19 16:08         ` Douglas Raillard
2019-06-20 13:04           ` Patrick Bellasi
2019-06-21 10:17             ` Quentin Perret
2019-06-21 10:22               ` Quentin Perret
2019-05-16 13:06     ` Douglas Raillard [this message]
2019-05-16 13:06       ` Douglas Raillard
2019-05-08 17:42 ` [RFC PATCH 2/7] sched/cpufreq: Attach perf domain to sugov policy douglas.raillard
2019-05-08 17:42   ` douglas.raillard
2019-05-08 17:42 ` [RFC PATCH 3/7] sched/cpufreq: Hook em_pd_get_higher_power() into get_next_freq() douglas.raillard
2019-05-08 17:42   ` douglas.raillard
2019-05-08 17:42 ` [RFC PATCH 4/7] sched/cpufreq: Move up sugov_cpu_is_busy() douglas.raillard
2019-05-08 17:42   ` douglas.raillard
2019-05-08 17:42 ` [RFC PATCH 5/7] sched/cpufreq: sugov_cpu_is_busy for shared policy douglas.raillard
2019-05-08 17:42   ` douglas.raillard
2019-05-08 17:43 ` [RFC PATCH 6/7] sched/cpufreq: Improve sugov_cpu_is_busy accuracy douglas.raillard
2019-05-08 17:43   ` douglas.raillard
2019-05-16 12:55   ` Patrick Bellasi
2019-05-16 12:55     ` Patrick Bellasi
2019-06-19 16:19     ` Douglas Raillard
2019-06-20 11:05       ` Patrick Bellasi
2019-05-08 17:43 ` [RFC PATCH 7/7] sched/cpufreq: Boost schedutil frequency ramp up douglas.raillard
2019-05-08 17:43   ` douglas.raillard
2019-05-13  7:12 ` [RFC PATCH 0/7] sched/cpufreq: Make schedutil energy aware Viresh Kumar
2019-05-13  7:12   ` Viresh Kumar
2019-05-13 13:52   ` Douglas Raillard
2019-05-13 13:52     ` Douglas Raillard

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