cpufreq: intel_pstate: Use IOWAIT flag in Atom algorithm

Modify the P-state selection algorithm for Atom processors to use
the new SCHED_CPUFREQ_IOWAIT flag instead of the questionable
get_cpu_iowait_time_us() function.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 31 insertions, 27 deletions

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index bdbe9369146b..7c457ccf9153 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -181,6 +181,8 @@ struct _pid {
  * @cpu:                CPU number for this instance data
  * @update_util:        CPUFreq utility callback information
  * @update_util_set:    CPUFreq utility callback is set
+ * @iowait_boost:       iowait-related boost fraction
+ * @last_update:        Time of the last update.
  * @pstate:             Stores P state limits for this CPU
  * @vid:                Stores VID limits for this CPU
  * @pid:                Stores PID parameters for this CPU
@@ -206,6 +208,7 @@ struct cpudata {
         struct vid_data vid;
         struct _pid pid;
 
+        u64     last_update;
         u64     last_sample_time;
         u64     prev_aperf;
         u64     prev_mperf;
@@ -216,6 +219,7 @@ struct cpudata {
         struct acpi_processor_performance acpi_perf_data;
         bool valid_pss_table;
 #endif
+        unsigned int iowait_boost;
 };
 
 static struct cpudata **all_cpu_data;
@@ -229,6 +233,7 @@ static struct cpudata **all_cpu_data;
  * @p_gain_pct:         PID proportional gain
  * @i_gain_pct:         PID integral gain
  * @d_gain_pct:         PID derivative gain
+ * @boost_iowait:       Whether or not to use iowait boosting.
  *
  * Stores per CPU model static PID configuration data.
  */
@@ -240,6 +245,7 @@ struct pstate_adjust_policy {
         int p_gain_pct;
         int d_gain_pct;
         int i_gain_pct;
+        bool boost_iowait;
 };
 
 /**
@@ -1037,6 +1043,7 @@ static struct cpu_defaults silvermont_params = {
                 .p_gain_pct = 14,
                 .d_gain_pct = 0,
                 .i_gain_pct = 4,
+                .boost_iowait = true,
         },
         .funcs = {
                 .get_max = atom_get_max_pstate,
@@ -1058,6 +1065,7 @@ static struct cpu_defaults airmont_params = {
                 .p_gain_pct = 14,
                 .d_gain_pct = 0,
                 .i_gain_pct = 4,
+                .boost_iowait = true,
         },
         .funcs = {
                 .get_max = atom_get_max_pstate,
@@ -1099,6 +1107,7 @@ static struct cpu_defaults bxt_params = {
                 .p_gain_pct = 14,
                 .d_gain_pct = 0,
                 .i_gain_pct = 4,
+                .boost_iowait = true,
         },
         .funcs = {
                 .get_max = core_get_max_pstate,
@@ -1222,36 +1231,18 @@ static inline int32_t get_avg_pstate(struct cpudata *cpu)
 static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
 {
         struct sample *sample = &cpu->sample;
-        u64 cummulative_iowait, delta_iowait_us;
-        u64 delta_iowait_mperf;
-        u64 mperf, now;
-        int32_t cpu_load;
+        int32_t busy_frac, boost;
 
-        cummulative_iowait = get_cpu_iowait_time_us(cpu->cpu, &now);
+        busy_frac = div_fp(sample->mperf, sample->tsc);
 
-        /*
-         * Convert iowait time into number of IO cycles spent at max_freq.
-         * IO is considered as busy only for the cpu_load algorithm. For
-         * performance this is not needed since we always try to reach the
-         * maximum P-State, so we are already boosting the IOs.
-         */
-        delta_iowait_us = cummulative_iowait - cpu->prev_cummulative_iowait;
-        delta_iowait_mperf = div64_u64(delta_iowait_us * cpu->pstate.scaling *
-                cpu->pstate.max_pstate, MSEC_PER_SEC);
+        boost = cpu->iowait_boost;
+        cpu->iowait_boost >>= 1;
 
-        mperf = cpu->sample.mperf + delta_iowait_mperf;
-        cpu->prev_cummulative_iowait = cummulative_iowait;
+        if (busy_frac < boost)
+                busy_frac = boost;
 
-        /*
-         * The load can be estimated as the ratio of the mperf counter
-         * running at a constant frequency during active periods
-         * (C0) and the time stamp counter running at the same frequency
-         * also during C-states.
-         */
-        cpu_load = div64_u64(int_tofp(100) * mperf, sample->tsc);
-        cpu->sample.busy_scaled = cpu_load;
-
-        return get_avg_pstate(cpu) - pid_calc(&cpu->pid, cpu_load);
+        sample->busy_scaled = busy_frac * 100;
+        return get_avg_pstate(cpu) - pid_calc(&cpu->pid, sample->busy_scaled);
 }
 
 static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
@@ -1332,8 +1323,21 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
                                      unsigned int flags)
 {
         struct cpudata *cpu = container_of(data, struct cpudata, update_util);
-        u64 delta_ns = time - cpu->sample.time;
+        u64 delta_ns;
+
+        if (pid_params.boost_iowait) {
+                if (flags & SCHED_CPUFREQ_IOWAIT) {
+                        cpu->iowait_boost = int_tofp(1);
+                } else if (cpu->iowait_boost) {
+                        /* Clear iowait_boost if the CPU may have been idle. */
+                        delta_ns = time - cpu->last_update;
+                        if (delta_ns > TICK_NSEC)
+                                cpu->iowait_boost = 0;
+                }
+                cpu->last_update = time;
+        }
 
+        delta_ns = time - cpu->sample.time;
         if ((s64)delta_ns >= pid_params.sample_rate_ns) {
                 bool sample_taken = intel_pstate_sample(cpu, time);