linux-kernel - Re: [PATCH] cpufreq, intel_pstate, set max_sysfs_pct and min_sysfs

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Date:	Wed, 07 Oct 2015 10:50:17 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq, intel_pstate, set max_sysfs_pct and min_sysfs_pct
 on governor switch



On 10/07/2015 08:18 AM, Prarit Bhargava wrote:
> 
> 
> On 10/06/2015 07:06 PM, Rafael J. Wysocki wrote:
>> On Wednesday, October 07, 2015 12:43:55 AM Rafael J. Wysocki wrote:
>>> On Tuesday, October 06, 2015 05:49:07 PM Prarit Bhargava wrote:
> 
> <snip>
> 
>>>>
>>>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>>>> index 3af9dd7..bb24458 100644
>>>> --- a/drivers/cpufreq/intel_pstate.c
>>>> +++ b/drivers/cpufreq/intel_pstate.c
>>>> @@ -986,6 +986,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>>>>  	if (!policy->cpuinfo.max_freq)
>>>>  		return -ENODEV;
>>>>  
>>>> +	limits.min_sysfs_pct = 0;
>>>> +	limits.max_sysfs_pct = 100;
>>>> +
>>>>  	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE &&
>>>>  	    policy->max >= policy->cpuinfo.max_freq) {
>>>>  		limits.min_policy_pct = 100;
>>>> @@ -1004,9 +1007,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>>>>  	limits.max_policy_pct = clamp_t(int, limits.max_policy_pct, 0 , 100);
>>>>  
>>>>  	/* Normalize user input to [min_policy_pct, max_policy_pct] */
>>>> -	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
>>>> +	limits.min_perf_pct = limits.min_policy_pct;
>>>>  	limits.min_perf_pct = min(limits.max_policy_pct, limits.min_perf_pct);
>>>> -	limits.max_perf_pct = min(limits.max_policy_pct, limits.max_sysfs_pct);
>>>> +	limits.max_perf_pct = limits.max_sysfs_pct;
>>
>> On a second thought, isn't that always 100?  If so, doesn't it basically discard
>> limits.max_policy_pct?
> 
> Wow :)  I think you're right and that definitely was an unintended consequence
> of this patch.  I also see that I can clean up the intel_pstate_set_policy()
> code a bit more.  I'll submit a 2-part v2.

Kristen,

There is a question here and I'm going to need your input on the answer.  The
question is whether or not a user can exceed the max_policy_pct or drop below
the min_policy_pct values via sysfs?

If "No, a user should not be able to exceed or go below those values", then IMO

limits.max_sysfs_pct should default to limits.max_policy_pct, and
limits.min_sysfs_pct should default to limits.min_policy_pct.

and I will adjust my patch accordingly.

P.
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