linux-kernel - Re: [PATCH v4 20/24] PM / devfreq: tegra30: Optimize upper average watermark selection

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Message-ID: <3c9c6a3a-8bce-d304-8472-029e6e673a99@samsung.com>
Date:   Fri, 19 Jul 2019 15:09:39 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 20/24] PM / devfreq: tegra30: Optimize upper average
 watermark selection

On 19. 7. 19. 오전 11:21, Dmitry Osipenko wrote:
> В Fri, 19 Jul 2019 11:06:05 +0900
> Chanwoo Choi <cw00.choi@...sung.com> пишет:
> 
>> On 19. 7. 19. 오전 10:59, Dmitry Osipenko wrote:
>>> В Fri, 19 Jul 2019 10:36:30 +0900
>>> Chanwoo Choi <cw00.choi@...sung.com> пишет:
>>>   
>>>> On 19. 7. 8. 오전 7:32, Dmitry Osipenko wrote:  
>>>>> I noticed that CPU may be crossing the dependency threshold very
>>>>> frequently for some workloads and this results in a lot of
>>>>> interrupts which could be avoided if MCALL client is keeping
>>>>> actual EMC frequency at a higher rate.
>>>>>
>>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>>> ---
>>>>>  drivers/devfreq/tegra30-devfreq.c | 23 ++++++++++++++++++-----
>>>>>  1 file changed, 18 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/tegra30-devfreq.c
>>>>> b/drivers/devfreq/tegra30-devfreq.c index
>>>>> c3cf87231d25..4d582809acb6 100644 ---
>>>>> a/drivers/devfreq/tegra30-devfreq.c +++
>>>>> b/drivers/devfreq/tegra30-devfreq.c @@ -314,7 +314,8 @@ static
>>>>> void tegra_actmon_get_lower_upper(struct tegra_devfreq *tegra, }
>>>>>  
>>>>>  static void tegra_devfreq_update_avg_wmark(struct tegra_devfreq
>>>>> *tegra,
>>>>> -					   struct
>>>>> tegra_devfreq_device *dev)
>>>>> +					   struct
>>>>> tegra_devfreq_device *dev,
>>>>> +					   unsigned long freq)
>>>>>  {
>>>>>  	unsigned long avg_threshold, lower, upper;
>>>>>  
>>>>> @@ -323,6 +324,15 @@ static void
>>>>> tegra_devfreq_update_avg_wmark(struct tegra_devfreq *tegra,
>>>>> avg_threshold = dev->config->avg_dependency_threshold;
>>>>> avg_threshold = avg_threshold * ACTMON_SAMPLING_PERIOD; 
>>>>> +	/*
>>>>> +	 * If cumulative EMC frequency selection is higher than
>>>>> the
>>>>> +	 * device's, then there is no need to set upper watermark
>>>>> to
>>>>> +	 * a lower value because it will result in unnecessary
>>>>> upper
>>>>> +	 * interrupts.
>>>>> +	 */
>>>>> +	if (freq * ACTMON_SAMPLING_PERIOD > upper)
>>>>> +		upper = freq * ACTMON_SAMPLING_PERIOD;    
>>>>
>>>> Also, 'upper value is used on the patch5. You can combine this code
>>>> to patch5 or if this patch depends on the cpu notifier, you can
>>>> combine it to the patch of adding cpu notifier without separate
>>>> patch.  
>>>
>>> Well okay, I'll try to squash some of the patches in the next
>>> revision. Usually I'm receiving comments in the other direction,
>>> asking to separate patches into smaller changes ;) So that's more a
>>> personal preference of each maintainer, I'd say.
>>>   
>>
>> Right. We have to make the patch with atomic attribute.
>> But, if there are patches which touch the same code
>> in the same patchset. We can squash or do refactorig
>> of this code.
> 
> The main benefit of having smaller logical changes is that when there is
> a bug, it's easier to narrow down the offending change using bisection.
> And it's just easier to review smaller patches, of course.

I agree that the patch should contain the atomic feature.
To remove the some communication confusion between us,
I don't mean that you have to merge patches to only one patch.

It is important to remove the following two cases on the same patchset.

1. the front patch adds the code and then later patch remove the added code.
2. the front patch changes the code and the later patch again modified
   the changed code of the front patch


> 
>> And also, if possible, I'd like you to make the patch
>> list according to the role of patch. For example,
>> the patches related to the 'watermark' could be sequentially
>> listed. But, it is not forced opinion. If just possible.
> 
> Okay, will take this into account.
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics