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

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Message-ID: <564F37C8.60307@redhat.com>
Date:	Fri, 20 Nov 2015 10:10:00 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
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 11/20/2015 08:18 AM, Viresh Kumar wrote:
> 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  ? :)

Oops -- and yeah, tested.  It works because I rewrite the value of
max_policy_pct :).  I'll repost shortly.

P.

> 
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