Re: [RFC][PATCH 0/3] New thermal interface allowing IPA to get max power

From: Chanwoo Choi <cw00.choi@samsung.com>
To: Lukasz Luba <lukasz.luba@arm.com>, daniel.lezcano@linaro.org
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	vireshk@kernel.org, rafael@kernel.org, Dietmar.Eggemann@arm.com,
	amitk@kernel.org, rui.zhang@intel.com, myungjoo.ham@samsung.com,
	kyungmin.park@samsung.com
Subject: Re: [RFC][PATCH 0/3] New thermal interface allowing IPA to get max power
Date: Tue, 2 Feb 2021 18:31:21 +0900	[thread overview]
Message-ID: <d05b247e-2294-e5f0-15bb-1a7a09a8e40e@samsung.com> (raw)
In-Reply-To: <5751adfa-6e25-3f3c-4a60-9b3c739fec1f@arm.com>

Hi Lukasz,

I'll review this patchset until tomorrow.

Thanks.
Chanwoo Choi 

On 2/1/21 8:23 PM, Lukasz Luba wrote:
> Daniel, Chanwoo
> 
> Gentle ping. Have you have a chance to check these patches?
> 
> On 1/26/21 10:39 AM, Lukasz Luba wrote:
>> Hi all,
>>
>> This patch set tries to add the missing feature in the Intelligent Power
>> Allocation (IPA) governor which is: frequency limit set by user space.
>> User can set max allowed frequency for a given device which has impact on
>> max allowed power. In current design there is no mechanism to figure this
>> out. IPA must know the maximum allowed power for every device. It is then
>> used for proper power split and divvy-up. When the user limit for max
>> frequency is not know, IPA assumes it is the highest possible frequency.
>> It causes wrong power split across the devices.
>>
>> This new mechanism provides the max allowed frequency to the thermal
>> framework and then max allowed power to the IPA.
>> The implementation is done in this way because currently there is no way
>> to retrieve the limits from the PM QoS, without uncapping the local
>> thermal limit and reading the next value. It would be a heavy way of
>> doing these things, since it should be done every polling time (e.g. 50ms).
>> Also, the value stored in PM QoS can be different than the real OPP 'rate'
>> so still would need conversion into proper OPP for comparison with EM.
>> Furthermore, uncapping the device in thermal just to check the user freq
>> limit is not the safest way.
>> Thus, this simple implementation moves the calculation of the proper
>> frequency to the sysfs write code, since it's called less often. The value
>> is then used as-is in the thermal framework without any hassle.
>>
>> As it's a RFC, it still misses the cpufreq sysfs implementation, but would
>> be addressed if all agree.
>>
>> Regards,
>> Lukasz Luba
>>
>> Lukasz Luba (3):
>>    PM /devfreq: add user frequency limits into devfreq struct
>>    thermal: devfreq_cooling: add new callback to get user limit for min
>>      state
>>    thermal: power_allocator: get proper max power limited by user
>>
>>   drivers/devfreq/devfreq.c             | 41 ++++++++++++++++++++++++---
>>   drivers/thermal/devfreq_cooling.c     | 33 +++++++++++++++++++++
>>   drivers/thermal/gov_power_allocator.c | 17 +++++++++--
>>   include/linux/devfreq.h               |  4 +++
>>   include/linux/thermal.h               |  1 +
>>   5 files changed, 90 insertions(+), 6 deletions(-)
>>
> 
> 

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics