linux-kernel - Re: [PATCH 4/5] intel_pstate: Use LFM bus ratio as min ratio/P state

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Message-ID: <5856987.3qKttR09W1@vostro.rjw.lan>
Date:	Wed, 19 Feb 2014 01:58:59 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	dirk.brandewie@...il.com
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH 4/5] intel_pstate: Use LFM bus ratio as min ratio/P state

On Wednesday, February 12, 2014 10:01:06 AM dirk.brandewie@...il.com wrote:
> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
> 
> Using LFM ratio provides better perf/watt vs min ratio.
> 
> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>

This changelog is particularly insufficient.

Can you please explain what's wrong with the previous calculation and how
the change makes it better?

> ---
>  drivers/cpufreq/intel_pstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index b80c03d..ff45ce1 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -356,7 +356,7 @@ static int byt_get_min_pstate(void)
>  {
>  	u64 value;
>  	rdmsrl(BYT_RATIOS, value);
> -	return value & 0xFF;
> +	return (value >> 8) & 0xFF;
>  }
>  
>  static int byt_get_max_pstate(void)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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