* [PATCH] cpufreq: intel_pstate: Improve accuracy by not truncating until final result
@ 2013-10-03 14:38 Brennan Shacklett
2013-10-10 14:55 ` Dirk Brandewie
0 siblings, 1 reply; 2+ messages in thread
From: Brennan Shacklett @ 2013-10-03 14:38 UTC (permalink / raw)
To: rjw, viresh.kumar, cpufreq, linux-kernel
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>
---
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] cpufreq: intel_pstate: Improve accuracy by not truncating until final result
2013-10-03 14:38 [PATCH] cpufreq: intel_pstate: Improve accuracy by not truncating until final result Brennan Shacklett
@ 2013-10-10 14:55 ` Dirk Brandewie
0 siblings, 0 replies; 2+ messages in thread
From: Dirk Brandewie @ 2013-10-10 14:55 UTC (permalink / raw)
To: Brennan Shacklett
Cc: rjw, viresh.kumar, cpufreq, linux-kernel, dirk.brandewie
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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