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Commit d5dd33d9 authored by Srinivas Pandruvada's avatar Srinivas Pandruvada Committed by Rafael J. Wysocki
Browse files

cpufreq: intel_pstate: increase precision of performance limits 



Even with round up of limits->min_perf and limits->max_perf, in some
cases resultant performance is 100 MHz less than the desired.

For example when the maximum frequency is 3.50 GHz, setting
scaling_min_frequency to 2.3 GHz always results in 2.2 GHz minimum.

Currently the fixed floating point operation uses 8 bit precision for
calculating limits->min_perf and limits->max_perf. For some operations
in this driver the 14 bit precision is used. Using the 14 bit precision
also for calculating limits->min_perf and limits->max_perf, addresses
this issue.

Introduced fp_ext_toint() equivalent to fp_toint() and int_ext_tofp()
equivalent to int_tofp() with 14 bit precision.

Signed-off-by: default avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 46992d6b

drivers/cpufreq/intel_pstate.c

+15 −13
Original line number Diff line number Diff line
@@ -54,6 +54,8 @@ 


#define EXT_BITS 6

#define EXT_FRAC_BITS (EXT_BITS + FRAC_BITS)

#define fp_ext_toint(X) ((X) >> EXT_FRAC_BITS)

#define int_ext_tofp(X) ((int64_t)(X) << EXT_FRAC_BITS)



static inline int32_t mul_fp(int32_t x, int32_t y)

{
@@ -351,9 +353,9 @@ static struct perf_limits performance_limits = { 
	.no_turbo = 0,

	.turbo_disabled = 0,

	.max_perf_pct = 100,

	.max_perf = int_tofp(1),

	.max_perf = int_ext_tofp(1),

	.min_perf_pct = 100,

	.min_perf = int_tofp(1),

	.min_perf = int_ext_tofp(1),

	.max_policy_pct = 100,

	.max_sysfs_pct = 100,

	.min_policy_pct = 0,
@@ -364,7 +366,7 @@ static struct perf_limits powersave_limits = { 
	.no_turbo = 0,

	.turbo_disabled = 0,

	.max_perf_pct = 100,

	.max_perf = int_tofp(1),

	.max_perf = int_ext_tofp(1),

	.min_perf_pct = 0,

	.min_perf = 0,

	.max_policy_pct = 100,
@@ -776,7 +778,7 @@ 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_fp(limits->max_perf_pct, 100);

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



	mutex_unlock(&intel_pstate_limits_lock);
@@ -804,7 +806,7 @@ 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_fp(limits->min_perf_pct, 100);

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



	mutex_unlock(&intel_pstate_limits_lock);
@@ -1189,11 +1191,11 @@ static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max) 
	 * policy, or by cpu specific default values determined through

	 * experimentation.

	 */

	max_perf_adj = fp_toint(max_perf * perf_limits->max_perf);

	max_perf_adj = fp_ext_toint(max_perf * perf_limits->max_perf);

	*max = clamp_t(int, max_perf_adj,

			cpu->pstate.min_pstate, cpu->pstate.turbo_pstate);



	min_perf = fp_toint(max_perf * perf_limits->min_perf);

	min_perf = fp_ext_toint(max_perf * perf_limits->min_perf);

	*min = clamp_t(int, min_perf, cpu->pstate.min_pstate, max_perf);

}
@@ -1561,9 +1563,9 @@ static void intel_pstate_set_performance_limits(struct perf_limits *limits) 
	limits->no_turbo = 0;

	limits->turbo_disabled = 0;

	limits->max_perf_pct = 100;

	limits->max_perf = int_tofp(1);

	limits->max_perf = int_ext_tofp(1);

	limits->min_perf_pct = 100;

	limits->min_perf = int_tofp(1);

	limits->min_perf = int_ext_tofp(1);

	limits->max_policy_pct = 100;

	limits->max_sysfs_pct = 100;

	limits->min_policy_pct = 0;
@@ -1602,10 +1604,10 @@ static void intel_pstate_update_perf_limits(struct cpufreq_policy *policy, 
	/* Make sure min_perf_pct <= max_perf_pct */

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



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

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

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

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

	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);



	mutex_unlock(&intel_pstate_limits_lock);