[PATCH v2, 3/3] intel_pstate: Clean up get_target_pstate_use_performance()

From: Rafael J. Wysocki
Date: Wed May 11 2016 - 13:10:04 EST


From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

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@xxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -1254,43 +1254,38 @@ static inline int32_t get_target_pstate_

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)