From: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
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: <stable@xxxxxxxxxxxxxxx> # 3.14.x
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index db8a992..c4dad16 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -58,6 +58,7 @@ struct sample {
u64 aperf;
u64 mperf;
int freq;
+ ktime_t time;
};
struct pstate_data {
@@ -93,6 +94,7 @@ struct cpudata {
struct vid_data vid;
struct _pid pid;
+ ktime_t last_sample_time;
u64 prev_aperf;
u64 prev_mperf;
struct sample sample;
@@ -576,6 +578,8 @@ 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;
@@ -598,12 +602,24 @@ 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;
}
--
1.9.0
--
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