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

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Date:   Fri, 19 Jul 2019 10:36:30 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        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>
Cc:     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. 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.

> +
>  	/*
>  	 * We want to get interrupts when MCCPU client crosses the
>  	 * dependency threshold in order to take into / out of account
> @@ -392,6 +402,7 @@ static void actmon_isr_device(struct tegra_devfreq *tegra,
>  			      struct tegra_devfreq_device *dev)
>  {
>  	u32 intr_status, dev_ctrl, avg_intr_mask, avg_count;
> +	unsigned long freq;
>  
>  	trace_device_isr_enter(tegra->regs, dev->config->offset,
>  			       dev->boost_freq, cpufreq_get(0));
> @@ -405,8 +416,10 @@ static void actmon_isr_device(struct tegra_devfreq *tegra,
>  	avg_intr_mask = ACTMON_DEV_INTR_AVG_BELOW_WMARK |
>  			ACTMON_DEV_INTR_AVG_ABOVE_WMARK;
>  
> -	if (intr_status & avg_intr_mask)
> -		tegra_devfreq_update_avg_wmark(tegra, dev);
> +	if (intr_status & avg_intr_mask) {
> +		freq = clk_get_rate(tegra->emc_clock) / KHZ;
> +		tegra_devfreq_update_avg_wmark(tegra, dev, freq);
> +	}
>  
>  	if (intr_status & ACTMON_DEV_INTR_CONSECUTIVE_UPPER) {
>  		/*
> @@ -525,7 +538,7 @@ static int tegra_actmon_clk_notify_cb(struct notifier_block *nb,
>  	for (i = 0; i < ARRAY_SIZE(tegra->devices); i++) {
>  		dev = &tegra->devices[i];
>  
> -		tegra_devfreq_update_avg_wmark(tegra, dev);
> +		tegra_devfreq_update_avg_wmark(tegra, dev, freq);
>  		tegra_devfreq_update_wmark(tegra, dev, freq);
>  	}
>  
> @@ -630,7 +643,7 @@ static void tegra_actmon_configure_device(struct tegra_devfreq *tegra,
>  	device_writel(dev, dev->avg_freq * ACTMON_SAMPLING_PERIOD,
>  		      ACTMON_DEV_INIT_AVG);
>  
> -	tegra_devfreq_update_avg_wmark(tegra, dev);
> +	tegra_devfreq_update_avg_wmark(tegra, dev, dev->avg_freq);
>  	tegra_devfreq_update_wmark(tegra, dev, dev->avg_freq);
>  
>  	device_writel(dev, ACTMON_COUNT_WEIGHT, ACTMON_DEV_COUNT_WEIGHT);
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics