From b8bd1581aa6110eb234c0d424eccd3f32d7317e6 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Thu, 7 Feb 2019 12:51:04 +0100 Subject: [PATCH] cpufreq: intel_pstate: Rework iowait boosting to be less aggressive The current iowait boosting mechanism in intel_pstate_update_util() is quite aggressive, as it goes to the maximum P-state right away, and may cause excessive amounts of energy to be used, which is not desirable and arguably isn't necessary too. Follow commit a5a0809bc58e ("cpufreq: schedutil: Make iowait boost more energy efficient") that reworked the analogous iowait boost mechanism in the schedutil governor and make the iowait boosting in intel_pstate_update_util() work along the same lines. Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/intel_pstate.c | 36 +++++++++++++++++----------------- 1 file changed, 18 insertions(+), 18 deletions(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 9a6cb3a1be50..002f5169d4eb 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -50,6 +50,8 @@ #define int_tofp(X) ((int64_t)(X) << FRAC_BITS) #define fp_toint(X) ((X) >> FRAC_BITS) +#define ONE_EIGHTH_FP ((int64_t)1 << (FRAC_BITS - 3)) + #define EXT_BITS 6 #define EXT_FRAC_BITS (EXT_BITS + FRAC_BITS) #define fp_ext_toint(X) ((X) >> EXT_FRAC_BITS) @@ -1671,17 +1673,14 @@ static inline int32_t get_avg_pstate(struct cpudata *cpu) static inline int32_t get_target_pstate(struct cpudata *cpu) { struct sample *sample = &cpu->sample; - int32_t busy_frac, boost; + int32_t busy_frac; int target, avg_pstate; busy_frac = div_fp(sample->mperf << cpu->aperf_mperf_shift, sample->tsc); - boost = cpu->iowait_boost; - cpu->iowait_boost >>= 1; - - if (busy_frac < boost) - busy_frac = boost; + if (busy_frac < cpu->iowait_boost) + busy_frac = cpu->iowait_boost; sample->busy_scaled = busy_frac * 100; @@ -1758,29 +1757,30 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time, if (smp_processor_id() != cpu->cpu) return; + delta_ns = time - cpu->last_update; if (flags & SCHED_CPUFREQ_IOWAIT) { - cpu->iowait_boost = int_tofp(1); - cpu->last_update = time; - /* - * The last time the busy was 100% so P-state was max anyway - * so avoid overhead of computation. - */ - if (fp_toint(cpu->sample.busy_scaled) == 100) - return; - - goto set_pstate; + /* Start over if the CPU may have been idle. */ + if (delta_ns > TICK_NSEC) { + cpu->iowait_boost = ONE_EIGHTH_FP; + } else if (cpu->iowait_boost) { + cpu->iowait_boost <<= 1; + if (cpu->iowait_boost > int_tofp(1)) + cpu->iowait_boost = int_tofp(1); + } else { + cpu->iowait_boost = ONE_EIGHTH_FP; + } } else if (cpu->iowait_boost) { /* Clear iowait_boost if the CPU may have been idle. */ - delta_ns = time - cpu->last_update; if (delta_ns > TICK_NSEC) cpu->iowait_boost = 0; + else + cpu->iowait_boost >>= 1; } cpu->last_update = time; delta_ns = time - cpu->sample.time; if ((s64)delta_ns < INTEL_PSTATE_SAMPLING_INTERVAL) return; -set_pstate: if (intel_pstate_sample(cpu, time)) intel_pstate_adjust_pstate(cpu); }