[PATCH 1/2] cpufreq: intel_pstate: round up min_perf limits

[PATCH 1/2] cpufreq: intel_pstate: round up min_perf limits

[Srinivas Pandruvada]

In some use cases, user wants to enforce a minimum performance limit on
CPUs. But because of simple division the resultant performance is 100 MHz
less than the desired in some cases.

For example when the maximum frequency is 3.50 GHz, setting
scaling_min_frequency to 1.6 GHz always results in 1.5 GHz minimum. With
simple round up, the frequency can be set to 1.6 GHz to minimum in this
case. This round up is already done to max_policy_pct and max_perf, so do
the same for min_policy_pct and min_perf.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 drivers/cpufreq/intel_pstate.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index f07e591..2f27812 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1569,8 +1569,8 @@ static void intel_pstate_update_perf_limits(struct cpufreq_policy *policy,
 	if (policy->max == policy->min) {
 		limits->min_policy_pct = limits->max_policy_pct;
 	} else {
-		limits->min_policy_pct = (policy->min * 100) /
-						policy->cpuinfo.max_freq;
+		limits->min_policy_pct = DIV_ROUND_UP(policy->min * 100,
+						      policy->cpuinfo.max_freq);
 		limits->min_policy_pct = clamp_t(int, limits->min_policy_pct,
 						 0, 100);
 	}
@@ -1591,6 +1591,7 @@ static void intel_pstate_update_perf_limits(struct cpufreq_policy *policy,
 	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);
 
 	mutex_unlock(&intel_pstate_limits_lock);
 
-- 
2.7.4

[PATCH 2/2] cpufreq: intel_pstate: increase precision of performance limits

[Srinivas Pandruvada]

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>
---
 drivers/cpufreq/intel_pstate.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 2f27812..72e8bbc 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -52,6 +52,8 @@
 
 #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)
 {
@@ -345,9 +347,9 @@ 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,
@@ -358,7 +360,7 @@ 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,
@@ -770,7 +772,7 @@ 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);
 
@@ -798,7 +800,7 @@ 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);
 
@@ -1183,11 +1185,11 @@ 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);
 }
 
@@ -1547,9 +1549,9 @@ 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;
@@ -1588,10 +1590,10 @@ 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);
 
-- 
2.7.4