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>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index bdbe9369146bb7cc2eec9a7aee84dc5f3e9ae49d..7c457ccf9153c62bbcda01e8a3056fe7097032c3 100644 (file)
--- 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);