From: Dirk Brandewie <[email protected]> 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: <[email protected]> # 3.14.x Signed-off-by: Dirk Brandewie <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
