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Commit e0d4c8f8 authored by Kristen Carlson Accardi's avatar Kristen Carlson Accardi Committed by Rafael J. Wysocki
Browse files

intel_pstate: Add a few comments 



Add a few comments in the code which calculates busyness to
clarify parts of the algorithm.

Signed-off-by: default avatarKristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent aa4ea34d

drivers/cpufreq/intel_pstate.c

+31 −1
Original line number Diff line number Diff line
@@ -199,7 +199,14 @@ static signed int pid_calc(struct _pid *pid, int32_t busy) 


	pid->integral += fp_error;



	/* limit the integral term */

	/*

	 * We limit the integral here so that it will never

	 * get higher than 30.  This prevents it from becoming

	 * too large an input over long periods of time and allows

	 * it to get factored out sooner.

	 *

	 * The value of 30 was chosen through experimentation.

	 */

	integral_limit = int_tofp(30);

	if (pid->integral > integral_limit)

		pid->integral = integral_limit;
@@ -616,6 +623,11 @@ static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max) 
	if (limits.no_turbo || limits.turbo_disabled)

		max_perf = cpu->pstate.max_pstate;



	/*

	 * performance can be limited by user through sysfs, by cpufreq

	 * policy, or by cpu specific default values determined through

	 * experimentation.

	 */

	max_perf_adj = fp_toint(mul_fp(int_tofp(max_perf), limits.max_perf));

	*max = clamp_t(int, max_perf_adj,

			cpu->pstate.min_pstate, cpu->pstate.turbo_pstate);
@@ -717,11 +729,29 @@ static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu) 
	u32 duration_us;

	u32 sample_time;



	/*

	 * 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.

	 */

	core_busy = cpu->sample.core_pct_busy;

	max_pstate = int_tofp(cpu->pstate.max_pstate);

	current_pstate = int_tofp(cpu->pstate.current_pstate);

	core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));



	/*

	 * Since we have a deferred timer, it will not fire unless

	 * we are in C0.  So, determine 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.

	 */

	sample_time = pid_params.sample_rate_ms  * USEC_PER_MSEC;

	duration_us = (u32) ktime_us_delta(cpu->sample.time,

					   cpu->last_sample_time);