Messages in this thread | | | Date | Thu, 10 Oct 2013 07:55:00 -0700 | From | Dirk Brandewie <> | Subject | Re: [PATCH] cpufreq: intel_pstate: Improve accuracy by not truncating until final result |
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On 10/03/2013 07:38 AM, Brennan Shacklett wrote: > From: Brennan Shacklett <brennan@genyes.org> > > 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@gmail.com> Acked-by: Dirk Brandewie <dirk.j.brandewie@intel.com> > --- > 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; >
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