Commit d253d2a5 authored by Brennan Shacklett's avatar Brennan Shacklett Committed by Rafael J. Wysocki
Browse files

intel_pstate: Improve accuracy by not truncating until final result 

This patch addresses Bug 60727
(https://bugzilla.kernel.org/show_bug.cgi?id=60727)
which was due to the truncation of intermediate values in the
calculations, which causes the code to consistently underestimate the
current cpu frequency, specifically 100% cpu utilization was truncated
down to the setpoint of 97%. This patch fixes the problem by keeping
the results of all intermediate calculations as fixed point numbers
rather scaling them back and forth between integers and fixed point.

References: https://bugzilla.kernel.org/show_bug.cgi?id=60727


Signed-off-by: default avatarBrennan Shacklett <bpshacklett@gmail.com>
Acked-by: default avatarDirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 31d141e3

drivers/cpufreq/intel_pstate.c

+15 −18
Original line number Diff line number Diff line
@@ -48,7 +48,7 @@ static inline int32_t div_fp(int32_t x, int32_t y) 
}



struct sample {

	int core_pct_busy;

	int32_t core_pct_busy;

	u64 aperf;

	u64 mperf;

	int freq;
@@ -68,7 +68,7 @@ struct _pid { 
	int32_t i_gain;

	int32_t d_gain;

	int deadband;

	int last_err;

	int32_t last_err;

};



struct cpudata {
@@ -153,16 +153,15 @@ static inline void pid_d_gain_set(struct _pid *pid, int percent) 
	pid->d_gain = div_fp(int_tofp(percent), int_tofp(100));

}



static signed int pid_calc(struct _pid *pid, int busy)

static signed int pid_calc(struct _pid *pid, int32_t busy)

{

	signed int err, result;

	signed int result;

	int32_t pterm, dterm, fp_error;

	int32_t integral_limit;



	err = pid->setpoint - busy;

	fp_error = int_tofp(err);

	fp_error = int_tofp(pid->setpoint) - busy;



	if (abs(err) <= pid->deadband)

	if (abs(fp_error) <= int_tofp(pid->deadband))

		return 0;



	pterm = mul_fp(pid->p_gain, fp_error);
@@ -176,8 +175,8 @@ static signed int pid_calc(struct _pid *pid, int busy) 
	if (pid->integral < -integral_limit)

		pid->integral = -integral_limit;



	dterm = mul_fp(pid->d_gain, (err - pid->last_err));

	pid->last_err = err;

	dterm = mul_fp(pid->d_gain, fp_error - pid->last_err);

	pid->last_err = fp_error;



	result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;
@@ -436,8 +435,9 @@ static inline void intel_pstate_calc_busy(struct cpudata *cpu, 
					struct sample *sample)

{

	u64 core_pct;

	core_pct = div64_u64(sample->aperf * 100, sample->mperf);

	sample->freq = cpu->pstate.max_pstate * core_pct * 1000;

	core_pct = div64_u64(int_tofp(sample->aperf * 100),

			     sample->mperf);

	sample->freq = fp_toint(cpu->pstate.max_pstate * core_pct * 1000);



	sample->core_pct_busy = core_pct;

}
@@ -469,22 +469,19 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu) 
	mod_timer_pinned(&cpu->timer, jiffies + delay);

}



static inline int intel_pstate_get_scaled_busy(struct cpudata *cpu)

static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)

{

	int32_t busy_scaled;

	int32_t core_busy, max_pstate, current_pstate;



	core_busy = int_tofp(cpu->samples[cpu->sample_ptr].core_pct_busy);

	core_busy = cpu->samples[cpu->sample_ptr].core_pct_busy;

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

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

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



	return fp_toint(busy_scaled);

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

}



static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)

{

	int busy_scaled;

	int32_t busy_scaled;

	struct _pid *pid;

	signed int ctl = 0;

	int steps;

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