linux-kernel - [PATCH 3/3] intel_pstate: Clean up get_target_pstate_use

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Date:	Sat, 07 May 2016 01:47:08 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/3] intel_pstate: Clean up get_target_pstate_use_performance()

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

The way the code in get_target_pstate_use_performance() is arranged
and the comments in there 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@...el.com>
---
 drivers/cpufreq/intel_pstate.c |   32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -1241,43 +1241,37 @@ 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, 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 (in percent) scaled by the ratio of the P-state requested
+	 * last time to the maximum P-state.  That measures the system's
+	 * response to the previous P-state selection.
 	 */
-	core_busy = 100 * cpu->sample.core_avg_perf;
-	max_pstate = cpu->pstate.max_pstate_physical;
-	current_pstate = cpu->pstate.current_pstate;
-	core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
+	perf_scaled = div_fp(cpu->pstate.max_pstate_physical,
+			     cpu->pstate.current_pstate);
+	perf_scaled = mul_fp(perf_scaled, 100 * cpu->sample.core_avg_perf);
 
 	/*
 	 * 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)