[PATCH 3.14 66/78] intel_pstate: add sample time scaling

Greg Kroah-Hartman
2014-06-09T23:02:09Z

From: Dirk Brandewie <dirk.j.brandewie@intel.com>

commit c4ee841f602e5eef8eab673295c49c5b49d7732b upstream.

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.

Signed-off-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>

---
drivers/cpufreq/intel_pstate.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -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(s
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_samp

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;
}