linux-kernel - Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

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Date:   Tue, 10 Dec 2019 08:28:12 +0100
From:   Kamil Konieczny <k.konieczny@...sung.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Subject: Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

On 10.12.2019 02:41, Chanwoo Choi wrote:
> On 12/9/19 11:44 PM, Kamil Konieczny wrote:
>> There is no need for creating another workqueue, it is enough
>> to reuse system_freezable_power_efficient one.
>>
>> Signed-off-by: Kamil Konieczny <k.konieczny@...sung.com>
>> ---
>>  drivers/devfreq/devfreq.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 46a7ff7c2994..955949c6fc1f 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>>  		return PTR_ERR(devfreq_class);
>>  	}
>>  
>> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
>> +	devfreq_wq = system_freezable_power_efficient_wq;
> 
> It affect the behaviors of whole device drivers using devfreq subsystem.
> It is not good to change the workqueue type without any reasonable
> data like experiment result, power-consumption result and performance
> result for almost device drivers using devfreq subsystem.
> 
> Are there any problem or any benefit to change workqueue type?

The workqueue is freezable with additional capability of 'power_efficient',
it is already developed by linux community so why not reuse it ?

> Actually, it is not simple to change the like just one device driver
> because devfreq subsytem is very important for both performance
> and power-consumption.

I agree. The name of this wq promises what you want, both freezable
and power efficiency.

> If you hope to change the feature related to both performance 
> and power-consumption, please suggest the reasonable data
> with fundamental reason.
> 
> So, I can't agree it.
> 
> 
>>  	if (!devfreq_wq) {
>>  		class_destroy(devfreq_class);
>> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
>> -		return -ENOMEM;
>> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
>> +		return -EINVAL;
>>  	}
>>  	devfreq_class->dev_groups = devfreq_groups;
>>  
>>
> 
> 

-- 
Best regards,
Kamil Konieczny
Samsung R&D Institute Poland