From: Brennan Shacklett <brennan@xxxxxxxxxx> 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. Signed-off-by: Brennan Shacklet <bpshacklett@xxxxxxxxx> --- Tested on my Intel Core i7 2640M which also suffered from bug 60727. It is possible that some of the constants in the default_policy should be changed, because I notice that my cpu tends to run slightly faster with this patch, which makes sense because calculated values would have been consistently low without the patch. drivers/cpufreq/intel_pstate.c | 33 +++++++++++++++------------------ 1 file changed, 15 insertions(+), 18 deletions(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 9733f29..2409f7f 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -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; @@ -432,8 +431,9 @@ 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; } @@ -465,22 +465,19 @@ 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; -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
