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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: Brennan Shacklett <bpshacklett@gmail.com> Acked-by: Dirk Brandewie <dirk.j.brandewie@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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parent
31d141e3a6
commit
d253d2a526
1 changed files with 15 additions and 18 deletions
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@ -48,7 +48,7 @@ static inline int32_t div_fp(int32_t x, int32_t y)
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}
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struct sample {
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int core_pct_busy;
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int32_t core_pct_busy;
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u64 aperf;
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u64 mperf;
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int freq;
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@ -68,7 +68,7 @@ struct _pid {
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int32_t i_gain;
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int32_t d_gain;
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int deadband;
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int last_err;
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int32_t last_err;
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};
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struct cpudata {
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@ -153,16 +153,15 @@ static inline void pid_d_gain_set(struct _pid *pid, int percent)
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pid->d_gain = div_fp(int_tofp(percent), int_tofp(100));
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}
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static signed int pid_calc(struct _pid *pid, int busy)
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static signed int pid_calc(struct _pid *pid, int32_t busy)
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{
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signed int err, result;
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signed int result;
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int32_t pterm, dterm, fp_error;
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int32_t integral_limit;
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err = pid->setpoint - busy;
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fp_error = int_tofp(err);
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fp_error = int_tofp(pid->setpoint) - busy;
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if (abs(err) <= pid->deadband)
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if (abs(fp_error) <= int_tofp(pid->deadband))
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return 0;
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pterm = mul_fp(pid->p_gain, fp_error);
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@ -176,8 +175,8 @@ static signed int pid_calc(struct _pid *pid, int busy)
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if (pid->integral < -integral_limit)
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pid->integral = -integral_limit;
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dterm = mul_fp(pid->d_gain, (err - pid->last_err));
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pid->last_err = err;
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dterm = mul_fp(pid->d_gain, fp_error - pid->last_err);
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pid->last_err = fp_error;
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result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;
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@ -436,8 +435,9 @@ static inline void intel_pstate_calc_busy(struct cpudata *cpu,
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struct sample *sample)
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{
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u64 core_pct;
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core_pct = div64_u64(sample->aperf * 100, sample->mperf);
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sample->freq = cpu->pstate.max_pstate * core_pct * 1000;
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core_pct = div64_u64(int_tofp(sample->aperf * 100),
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sample->mperf);
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sample->freq = fp_toint(cpu->pstate.max_pstate * core_pct * 1000);
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sample->core_pct_busy = core_pct;
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}
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@ -469,22 +469,19 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
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mod_timer_pinned(&cpu->timer, jiffies + delay);
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}
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static inline int intel_pstate_get_scaled_busy(struct cpudata *cpu)
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static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
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{
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int32_t busy_scaled;
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int32_t core_busy, max_pstate, current_pstate;
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core_busy = int_tofp(cpu->samples[cpu->sample_ptr].core_pct_busy);
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core_busy = cpu->samples[cpu->sample_ptr].core_pct_busy;
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max_pstate = int_tofp(cpu->pstate.max_pstate);
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current_pstate = int_tofp(cpu->pstate.current_pstate);
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busy_scaled = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
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return fp_toint(busy_scaled);
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return mul_fp(core_busy, div_fp(max_pstate, current_pstate));
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}
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static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)
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{
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int busy_scaled;
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int32_t busy_scaled;
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struct _pid *pid;
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signed int ctl = 0;
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int steps;
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