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: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e5ef51d7be4ea7338ccbb3d111cc1b7fc7559740..7159dbde016063be2d1dac67c950d76cd38311a1 100644 (file)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -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);