Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | [PATCH v2] cpufreq: intel_pstate: Rework iowait boosting to be less aggressive | Date | Thu, 07 Feb 2019 12:51:04 +0100 |
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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 <rafael.j.wysocki@intel.com> ---
-> v2: * Follow the Doug's suggestion and drop the immediate jump to max P-state if boost is max. The code is simpler this way and the perf impact should not be noticeable on average.
--- drivers/cpufreq/intel_pstate.c | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-)
Index: linux-pm/drivers/cpufreq/intel_pstate.c =================================================================== --- linux-pm.orig/drivers/cpufreq/intel_pstate.c +++ linux-pm/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) @@ -1679,17 +1681,14 @@ static inline int32_t get_avg_pstate(str 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; @@ -1768,29 +1767,30 @@ static void intel_pstate_update_util(str 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); }
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