linux-kernel - Re: [PATCH v7 18/19] PM / devfreq: tegra30: Tune up MCCPU boost-down coefficient

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Message-ID: <99a90972-2170-ebcb-7bff-cd9ba8b0b0d1@samsung.com>
Date:   Fri, 1 Nov 2019 16:45:40 +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>,
        Peter Geis <pgwipeout@...il.com>
Cc:     linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 18/19] PM / devfreq: tegra30: Tune up MCCPU
 boost-down coefficient

On 19. 10. 30. 오전 7:00, Dmitry Osipenko wrote:
> MCCPU boosts up very aggressively by 800% and boosts down very mildly by
> 10%. This doesn't work well when system is idling because the very slow
> de-boosting results in lots of consecutive-down interrupts, in result
> memory stays clocked high and CPU doesn't enter deepest idling state
> instead of keeping memory at lowest freq and having CPU cluster turned
> off. A more faster de-boosting fixes the case of idling system and doesn't
> affect the case of an active system.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra30-devfreq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
> index d0dd42856e5b..9a21a29198ee 100644
> --- a/drivers/devfreq/tegra30-devfreq.c
> +++ b/drivers/devfreq/tegra30-devfreq.c
> @@ -123,7 +123,7 @@ static const struct tegra_devfreq_device_config actmon_device_configs[] = {
>  		.offset = 0x200,
>  		.irq_mask = 1 << 25,
>  		.boost_up_coeff = 800,
> -		.boost_down_coeff = 90,
> +		.boost_down_coeff = 40,
>  		.boost_up_threshold = 27,
>  		.boost_down_threshold = 10,
>  		.avg_dependency_threshold = 50000,
> 

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

IMO, I think that it is not good to change the threshold value
on device driver directly when some requirement happen.
Instead, better to get the threshold value from device-tree file.


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics