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Date: Tue, 14 Mar 2017 16:18:34 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Linux PM <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/3] cpufreq: intel_pstate: Avoid percentages in limits-related computations
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
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 into 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: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
drivers/cpufreq/intel_pstate.c | 60 ++++++++++++++++++++---------------------
1 file changed, 30 insertions(+), 30 deletions(-)
Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -84,6 +84,11 @@ static inline u64 div_ext_fp(u64 x, u64
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
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
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
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
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_ut
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,
- policy->cpuinfo.max_freq);
- limits->min_policy_pct = clamp_t(int, limits->min_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);
- 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);
+ min_policy_perf = div_ext_fp(policy->min,
+ policy->cpuinfo.max_freq);
+ min_policy_perf = clamp_t(int32_t, min_policy_perf,
+ 0, max_policy_perf);
+ }
+
+ /* 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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