intel_pstate: Clean up get_target_pstate_use_performance()

The comments and the core_busy variable name in
get_target_pstate_use_performance() are totally confusing,
so modify them to reflect what's going on.

The results of the computations should be the same as before.

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

1 files changed, 11 insertions, 16 deletions

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index ff5c591578ee..b76a98dd9988 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1259,43 +1259,38 @@ static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
 
 static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
 {
-        int32_t core_busy, max_pstate, current_pstate, sample_ratio;
+        int32_t perf_scaled, max_pstate, current_pstate, sample_ratio;
         u64 duration_ns;
 
         /*
-         * core_busy is the ratio of actual performance to max
-         * max_pstate is the max non turbo pstate available
-         * current_pstate was the pstate that was requested during
-         *      the last sample period.
-         *
-         * We normalize core_busy, which was our actual percent
-         * performance to what we requested during the last sample
-         * period. The result will be a percentage of busy at a
-         * specified pstate.
+         * perf_scaled is the average performance during the last sampling
+         * period scaled by the ratio of the maximum P-state to the P-state
+         * requested last time (in percent).  That measures the system's
+         * response to the previous P-state selection.
          */
         max_pstate = cpu->pstate.max_pstate_physical;
         current_pstate = cpu->pstate.current_pstate;
-        core_busy = mul_ext_fp(cpu->sample.core_avg_perf,
+        perf_scaled = mul_ext_fp(cpu->sample.core_avg_perf,
                                div_fp(100 * max_pstate, current_pstate));
 
         /*
          * Since our utilization update callback will not run unless we are
          * in C0, check if the actual elapsed time is significantly greater (3x)
          * than our sample interval.  If it is, then we were idle for a long
-         * enough period of time to adjust our busyness.
+         * enough period of time to adjust our performance metric.
          */
         duration_ns = cpu->sample.time - cpu->last_sample_time;
         if ((s64)duration_ns > pid_params.sample_rate_ns * 3) {
                 sample_ratio = div_fp(pid_params.sample_rate_ns, duration_ns);
-                core_busy = mul_fp(core_busy, sample_ratio);
+                perf_scaled = mul_fp(perf_scaled, sample_ratio);
         } else {
                 sample_ratio = div_fp(100 * cpu->sample.mperf, cpu->sample.tsc);
                 if (sample_ratio < int_tofp(1))
-                        core_busy = 0;
+                        perf_scaled = 0;
         }
 
-        cpu->sample.busy_scaled = core_busy;
-        return cpu->pstate.current_pstate - pid_calc(&cpu->pid, core_busy);
+        cpu->sample.busy_scaled = perf_scaled;
+        return cpu->pstate.current_pstate - pid_calc(&cpu->pid, perf_scaled);
 }
 
 static inline void intel_pstate_update_pstate(struct cpudata *cpu, int pstate)