linux-kernel - Re: [PATCH v7 17/19] PM / devfreq: tegra30: Support variable polling interval

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Message-ID: <71a16d74-5908-ea97-ae98-4b7d0e99a765@gmail.com>
Date:   Sun, 3 Nov 2019 18:25:19 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Peter Geis <pgwipeout@...il.com>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 17/19] PM / devfreq: tegra30: Support variable polling
 interval

02.11.2019 01:23, Dmitry Osipenko пишет:
> 02.11.2019 00:58, Michał Mirosław пишет:
>> On Wed, Oct 30, 2019 at 01:00:17AM +0300, Dmitry Osipenko wrote:
>>> The ACTMON governor is interrupt-driven and currently hardware's polling
>>> interval is fixed to 16ms in the driver. Devfreq supports variable polling
>>> interval by the generic governors, let's re-use the generic interface for
>>> changing of the polling interval. Now the polling interval can be changed
>>> dynamically via /sys/class/devfreq/devfreq0/polling_interval.
>> [...]
>>> @@ -308,7 +308,7 @@ static unsigned long actmon_device_target_freq(struct tegra_devfreq *tegra,
>>>  	unsigned int avg_sustain_coef;
>>>  	unsigned long target_freq;
>>>  
>>> -	target_freq = dev->avg_count / ACTMON_SAMPLING_PERIOD;
>>> +	target_freq = dev->avg_count / tegra->devfreq->profile->polling_ms;
>>>  	avg_sustain_coef = 100 * 100 / dev->config->boost_up_threshold;
>>>  	target_freq = do_percent(target_freq, avg_sustain_coef);
>>>  	target_freq += dev->boost_freq;
>>
>> Noting a comment in patch 13, if this is hot path you could try reciprocal_divide().
> 
> Hello Michał,
> 
> This not really a hot path, I just wanted to optimize that case to keep
> things a bit nicer.
> 
> Please take a look at the arch/arm/boot/compressed/lib1funcs.S, firstly
> it checks whether divisor is a power of 2 value and then takes optimized
> code path that uses a single shift. Hence the patch 13 still applies here.

On the other hand, there is now only a single case of the division by
polling_ms in the driver which won't bring much benefit, so it indeed
makes sense to skip the patch 13 for now.