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intel_pstate: add sample time scaling 

The PID assumes that samples are of equal time, which for a deferable
timers this is not true when the system goes idle.  This causes the
PID to take a long time to converge to the min P state and depending
on the pattern of the idle load can make the P state appear stuck.

The hold-off value of three sample times before using the scaling is
to give a grace period for applications that have high performance
requirements and spend a lot of time idle,  The poster child for this
behavior is the ffmpeg benchmark in the Phoronix test suite.

Cc: 3.14+ <stable@vger.kernel.org> # 3.14+
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Dirk Brandewie 2014-05-29 09:32:24 -07:00 committed by Rafael J. Wysocki
parent f0fe3cd7e1
commit c4ee841f60
1 changed files with 17 additions and 1 deletions
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18
drivers/cpufreq/intel_pstate.c
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@ -60,6 +60,7 @@ struct sample {
u64 aperf;
u64 mperf;
int freq;
ktime_t time;
};
struct pstate_data {
@ -97,6 +98,7 @@ struct cpudata {
struct vid_data vid;
struct _pid pid;
ktime_t last_sample_time;
u64 prev_aperf;
u64 prev_mperf;
struct sample sample;
@ -583,6 +585,8 @@ static inline void intel_pstate_sample(struct cpudata *cpu)
aperf = aperf >> FRAC_BITS;
mperf = mperf >> FRAC_BITS;
cpu->last_sample_time = cpu->sample.time;
cpu->sample.time = ktime_get();
cpu->sample.aperf = aperf;
cpu->sample.mperf = mperf;
cpu->sample.aperf -= cpu->prev_aperf;
@ -605,12 +609,24 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
{
int32_t core_busy, max_pstate, current_pstate;
int32_t core_busy, max_pstate, current_pstate, sample_ratio;
u32 duration_us;
u32 sample_time;
core_busy = cpu->sample.core_pct_busy;
max_pstate = int_tofp(cpu->pstate.max_pstate);
current_pstate = int_tofp(cpu->pstate.current_pstate);
core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
sample_time = (pid_params.sample_rate_ms * USEC_PER_MSEC);
duration_us = (u32) ktime_us_delta(cpu->sample.time,
cpu->last_sample_time);
if (duration_us > sample_time * 3) {
sample_ratio = div_fp(int_tofp(sample_time),
int_tofp(duration_us));
core_busy = mul_fp(core_busy, sample_ratio);
}
return core_busy;
}