Commit e4c204ce authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

cpufreq: intel_pstate: Avoid percentages in limits-related computations 



Currently, intel_pstate_update_perf_limits() first converts the
policy minimum and maximum limits into percentages of the maximum
turbo frequency (rounding up to an integer) and then converts these
percentages to fractions (by using fixed-point arithmetic to divide
them by 100).

That introduces a rounding error unnecessarily, because the fractions
can be obtained by carrying out fixed-point divisions directly on the
input numbers.

Rework the computations in intel_pstate_hwp_set() to use fractions
instead of percentages (and drop redundant local variables from
there) and modify intel_pstate_update_perf_limits() to compute the
fractions directly and percentages out of them.

While at it, introduce percent_ext_fp() for converting percentages
to fractions (with extended number of fraction bits) and use it in
the computations.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 3f8ed54a

drivers/cpufreq/intel_pstate.c

+28 −28
Original line number Diff line number Diff line
@@ -84,6 +84,11 @@ static inline u64 div_ext_fp(u64 x, u64 y) 
	return div64_u64(x << EXT_FRAC_BITS, y);

}



static inline int32_t percent_ext_fp(int percent)

{

	return div_ext_fp(percent, 100);

}



/**

 * struct sample -	Store performance sample

 * @core_avg_perf:	Ratio of APERF/MPERF which is the actual average
@@ -850,7 +855,6 @@ static void intel_pstate_hwp_set(struct cpufreq_policy *policy) 
	u64 value, cap;



	for_each_cpu(cpu, policy->cpus) {

		int max_perf_pct, min_perf_pct;

		struct cpudata *cpu_data = all_cpu_data[cpu];

		s16 epp;
@@ -864,16 +868,14 @@ static void intel_pstate_hwp_set(struct cpufreq_policy *policy) 
		else

			hw_max = HWP_HIGHEST_PERF(cap);



		max_perf_pct = perf_limits->max_perf_pct;

		min_perf_pct = perf_limits->min_perf_pct;

		min = hw_max * min_perf_pct / 100;

		min = fp_ext_toint(hw_max * perf_limits->min_perf);



		rdmsrl_on_cpu(cpu, MSR_HWP_REQUEST, &value);



		value &= ~HWP_MIN_PERF(~0L);

		value |= HWP_MIN_PERF(min);



		max = hw_max * max_perf_pct / 100;

		max = fp_ext_toint(hw_max * perf_limits->max_perf);

		value &= ~HWP_MAX_PERF(~0L);

		value |= HWP_MAX_PERF(max);
@@ -1223,7 +1225,7 @@ static ssize_t store_max_perf_pct(struct kobject *a, struct attribute *b, 
				   limits->max_perf_pct);

	limits->max_perf_pct = max(limits->min_perf_pct,

				   limits->max_perf_pct);

	limits->max_perf = div_ext_fp(limits->max_perf_pct, 100);

	limits->max_perf = percent_ext_fp(limits->max_perf_pct);



	intel_pstate_update_policies();
@@ -1260,7 +1262,7 @@ static ssize_t store_min_perf_pct(struct kobject *a, struct attribute *b, 
				   limits->min_perf_pct);

	limits->min_perf_pct = min(limits->max_perf_pct,

				   limits->min_perf_pct);

	limits->min_perf = div_ext_fp(limits->min_perf_pct, 100);

	limits->min_perf = percent_ext_fp(limits->min_perf_pct);



	intel_pstate_update_policies();
@@ -2078,36 +2080,34 @@ static void intel_pstate_clear_update_util_hook(unsigned int cpu) 
static void intel_pstate_update_perf_limits(struct cpufreq_policy *policy,

					    struct perf_limits *limits)

{

	int32_t max_policy_perf, min_policy_perf;



	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);

	max_policy_perf = div_ext_fp(policy->max, policy->cpuinfo.max_freq);

	max_policy_perf = clamp_t(int32_t, max_policy_perf, 0, int_ext_tofp(1));

	if (policy->max == policy->min) {

		limits->min_policy_pct = limits->max_policy_pct;

		min_policy_perf = max_policy_perf;

	} else {

		limits->min_policy_pct = DIV_ROUND_UP(policy->min * 100,

		min_policy_perf = div_ext_fp(policy->min,

					     policy->cpuinfo.max_freq);

		limits->min_policy_pct = clamp_t(int, limits->min_policy_pct,

						 0, 100);

		min_policy_perf = clamp_t(int32_t, min_policy_perf,

					  0, max_policy_perf);

	}



	/* 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 = 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 = max(limits->min_policy_pct,

				   limits->max_perf_pct);

	/* Normalize user input to [min_perf, max_perf] */

	limits->min_perf = max(min_policy_perf,

			       percent_ext_fp(limits->min_sysfs_pct));

	limits->min_perf = min(limits->min_perf, max_policy_perf);

	limits->max_perf = min(max_policy_perf,

			       percent_ext_fp(limits->max_sysfs_pct));

	limits->max_perf = max(min_policy_perf, limits->max_perf);



	/* Make sure min_perf_pct <= max_perf_pct */

	limits->min_perf_pct = min(limits->max_perf_pct, limits->min_perf_pct);

	/* Make sure min_perf <= max_perf */

	limits->min_perf = min(limits->min_perf, limits->max_perf);



	limits->min_perf = div_ext_fp(limits->min_perf_pct, 100);

	limits->max_perf = div_ext_fp(limits->max_perf_pct, 100);

	limits->max_perf = round_up(limits->max_perf, EXT_FRAC_BITS);

	limits->min_perf = round_up(limits->min_perf, EXT_FRAC_BITS);

	limits->max_perf_pct = fp_ext_toint(limits->max_perf * 100);

	limits->min_perf_pct = fp_ext_toint(limits->min_perf * 100);



	pr_debug("cpu:%d max_perf_pct:%d min_perf_pct:%d\n", policy->cpu,

		 limits->max_perf_pct, limits->min_perf_pct);

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