linux-kernel - Re: [PATCH v4 16/37] PM / devfreq: tegra20: Adjust clocks conversion ratio and polling interval

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Date:   Thu, 2 Jul 2020 10:37:34 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Mikko Perttunen <cyndis@...si.fi>
Cc:     Artur Świgoń <a.swigon@...sung.com>,
        linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 16/37] PM / devfreq: tegra20: Adjust clocks
 conversion ratio and polling interval

On 6/9/20 10:13 PM, Dmitry Osipenko wrote:
> The current conversion ratio results in a higher frequency than needed,
> that is not very actual now since the Display Controller driver got
> support for memory bandwidth management and hence memory frequency can
> go lower now without bad consequences. Since memory freq now goes to a
> lower rates, the responsiveness of interactive applications become worse
> due to a quite high polling interval value that is currently set to 500ms.
> Changing polling interval to 30ms results in a good responsiveness of the
> system.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra20-devfreq.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/devfreq/tegra20-devfreq.c b/drivers/devfreq/tegra20-devfreq.c
> index 249d0dc44f6c..7cdea4ba38f7 100644
> --- a/drivers/devfreq/tegra20-devfreq.c
> +++ b/drivers/devfreq/tegra20-devfreq.c
> @@ -79,16 +79,12 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
>  
>  	/*
>  	 * EMC_COUNT returns number of memory events, that number is lower
> -	 * than the number of clocks. Conversion ratio of 1/8 results in a
> -	 * bit higher bandwidth than actually needed, it is good enough for
> -	 * the time being because drivers don't support requesting minimum
> -	 * needed memory bandwidth yet.
> -	 *
> -	 * TODO: adjust the ratio value once relevant drivers will support
> -	 * memory bandwidth management.
> +	 * than the number of total EMC clocks over the sampling period.
> +	 * The clocks number is converted to maximum possible number of
> +	 * memory events using the ratio of 1/4.
>  	 */
>  	stat->busy_time = readl_relaxed(tegra->regs + MC_STAT_EMC_COUNT);
> -	stat->total_time = readl_relaxed(tegra->regs + MC_STAT_EMC_CLOCKS) / 8;
> +	stat->total_time = readl_relaxed(tegra->regs + MC_STAT_EMC_CLOCKS) / 4;
>  	stat->current_frequency = clk_get_rate(tegra->emc_clock);
>  
>  	writel_relaxed(EMC_GATHER_CLEAR, tegra->regs + MC_STAT_CONTROL);
> @@ -98,7 +94,7 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
>  }
>  
>  static struct devfreq_dev_profile tegra_devfreq_profile = {
> -	.polling_ms	= 500,
> +	.polling_ms	= 30,
>  	.target		= tegra_devfreq_target,
>  	.get_dev_status	= tegra_devfreq_get_dev_status,
>  };
> 

Ackded-by: Chanwoo Choi <cw00.choi@...sung.com>

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics