linux-kernel - Re: [PATCH v4 05/16] PM / devfreq: tegra: Don't set EMC clock rate to maximum on probe

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Date:   Tue, 4 Jun 2019 13:00:42 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.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 05/16] PM / devfreq: tegra: Don't set EMC clock rate
 to maximum on probe

On Thu, May 02, 2019 at 02:38:04AM +0300, Dmitry Osipenko wrote:
> There is no real benefit from doing so, hence let's drop that rate setting
> for consistency.
> 
> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra-devfreq.c | 2 --
>  1 file changed, 2 deletions(-)

Do you have any numbers to tell how long it would take for the EMC rate
to get incremented? My understanding is that ACTMON basically reacts to
system load, so I could imagine that not setting to the maximum
frequency after this is loaded might make the system slow in the short
term. Only after ACTMON has collected enough data to determine that it
needs to clock the EMC higher would system speed resume normal.

I guess technically this patch doesn't change anything if the system
already boots at the highest EMC frequency anyway, which I think it does
on many (although not all) devices.

Anyway, you said you've tested this and are satisfied with the
performance, so it can't be that bad:

Acked-by: Thierry Reding <treding@...dia.com>

> 
> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
> index c7428c5eee23..24ec65556c39 100644
> --- a/drivers/devfreq/tegra-devfreq.c
> +++ b/drivers/devfreq/tegra-devfreq.c
> @@ -653,8 +653,6 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  		return PTR_ERR(tegra->emc_clock);
>  	}
>  
> -	clk_set_rate(tegra->emc_clock, ULONG_MAX);
> -
>  	tegra->rate_change_nb.notifier_call = tegra_actmon_rate_notify_cb;
>  	err = clk_notifier_register(tegra->emc_clock, &tegra->rate_change_nb);
>  	if (err) {
> -- 
> 2.21.0
> 

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