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authorBrennan Shacklett <brennan@genyes.org>2013-10-21 09:20:32 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-02-13 13:48:04 -0800
commite34ce30f3226936bf8f43dc3d2616acd268a8cd2 (patch)
tree163e64e7cc930711c6502d6403beec54a7a5a75c
parent3dc642a3984abb4e34b7514a5d569a50402410b7 (diff)
downloadlinaro-lsk-e34ce30f3226936bf8f43dc3d2616acd268a8cd2.tar.gz
intel_pstate: Improve accuracy by not truncating until final result
commit d253d2a52676cfa3d89b8f0737a08ce7db665207 upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/cpufreq/intel_pstate.c33
1 files changed, 15 insertions, 18 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index ac3ff4d..f82563d 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;
@@ -435,8 +434,9 @@ 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;
}
@@ -468,22 +468,19 @@ 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;