linux-kernel - Re: [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy

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Date:	Fri, 20 Nov 2015 18:48:33 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
	Len Brown <len.brown@...el.com>,
	Alexandra Yates <alexandra.yates@...el.com>,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy_pct
 rounding error

On 20-11-15, 07:32, Prarit Bhargava wrote:
> I have a Intel (6,63) processor with a "marketing" frequency (from
> /proc/cpuinfo) of 2100MHz, and a max turbo frequency of 2600MHz.  I
> can execute
> 
> cpupower frequency-set -g powersave --min 1200MHz --max 2100MHz
> 
> and the max_freq_pct is set to 80.  When adding load to the system I noticed
> that the cpu frequency only reached 2000MHZ and not 2100MHz as expected.
> 
> This is because limits->max_policy_pct is calculated as 2100 * 100 /2600 = 80.7
> and is rounded down to 80 when it should be rounded up to 81.  This patch
> adds a DIV_ROUND_UP() which will return the correct value.
> 
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...el.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Alexandra Yates <alexandra.yates@...el.com>
> Cc: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: linux-pm@...r.kernel.org
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 001a532..6b63374 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1110,6 +1110,8 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>  	limits->min_policy_pct = clamp_t(int, limits->min_policy_pct, 0 , 100);
>  	limits->max_policy_pct = (policy->max * 100) / policy->cpuinfo.max_freq;

Forgot to remove this line ?

>  	limits->max_policy_pct = clamp_t(int, limits->max_policy_pct, 0 , 100);

And put this after the later one ?

> +	limits->max_policy_pct = DIV_ROUND_UP(policy->max * 100,
> +					      policy->cpuinfo.max_freq);
>  
>  	/* Normalize user input to [min_policy_pct, max_policy_pct] */
>  	limits->min_perf_pct = max(limits->min_policy_pct,

Sure you tested it  ? :)

-- 
viresh
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