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

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Date:	Fri, 20 Nov 2015 20:02:37 +0000
From:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:	"prarit@...hat.com" <prarit@...hat.com>
CC:	"Brown, Len" <len.brown@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"kristen@...ux.intel.com" <kristen@...ux.intel.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"Yates, Alexandra" <alexandra.yates@...el.com>
Subject: Re: [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy_pct
 rounding error

On Fri, 2015-11-20 at 10:43 -0500, Prarit Bhargava wrote:
> 
> On 11/20/2015 10:19 AM, Viresh Kumar wrote:
> > On 20-11-15, 10:10, Prarit Bhargava wrote:
> >>>>  	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.
> > 
> > But we aren't doing below anymore, doesn't this change the
> > calculations at all?
> > 
> >   	limits->max_policy_pct = clamp_t(int, limits->max_policy_pct, 0 , 100);
> 
> The clamp only confines the max_policy between 0 and 100.  AFAIK it doesn't make
> any change tothe value of limits->max_policy_pct unless it was outside of that
> range.
> 
> P.
> > 

With the changes below (as suggested above), I did tests. Except two
cases, it did correct. Those two are in turbo range, so I am OK with
that. 


diff --git a/drivers/cpufreq/intel_pstate.c
b/drivers/cpufreq/intel_pstate.c
index b78abe9..c3bcca4 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1111,9 +1111,9 @@ static int intel_pstate_set_policy(struct
cpufreq_policy *policy)
 	limits = &powersave_limits;
 	limits->min_policy_pct = (policy->min * 100) /
policy->cpuinfo.max_freq;
 	limits->min_policy_pct = clamp_t(int, limits->min_policy_pct, 0 ,
100);
-	limits->max_policy_pct = (policy->max * 100) /
policy->cpuinfo.max_freq;
+	limits->max_policy_pct = DIV_ROUND_UP(policy->max * 100,
+                                             policy->cpuinfo.max_freq);
 	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);
@@ -1131,7 +1131,7 @@ static int intel_pstate_set_policy(struct
cpufreq_policy *policy)
 				  int_tofp(100));
 	limits->max_perf = div_fp(int_tofp(limits->max_perf_pct),
 				  int_tofp(100));
-
+	limits->max_perf = round_up(limits->max_perf, 8);
 	if (hwp_active)
 		intel_pstate_hwp_set();


3300 : OK
3200 : 1 less
3100 : 1 less
3000 : 1 less
2900 : OK
2800 : OK
2700 : OK
2600 : OK
2500 : OK
2400 : OK
2300 : OK
2200 : OK
2100 : OK
2000 : OK
1900 : OK
1800 : OK
1700 : OK
1600 : OK
1500 : OK
1400 : OK
1300 : OK
1200 : OK
1100 : OK
1000 : OK
900  : OK
800 : OK

Thanks,
Srinivas