v2 This is a much simpler version than the previous one and only consider IO boost, using the existing mechanism. There is no change in this series beyond intel_pstate driver.
Once PeterZ finishes his work on frequency invariant, I will revisit thread migration optimization in HWP mode. Other changes: - Gradual boost instead of single step as suggested by PeterZ. - Cross CPU synchronization concerns identified by Rafael. - Split the patch for HWP MSR value caching as suggested by PeterZ. Not changed as suggested: There is no architecture way to identify platform with Per-core P-states, so still have to enable feature based on CPU model. ----------- v1 This series tries to address some concern in performance particularly with IO workloads (Reported by Mel Gorman), when HWP is using intel_pstate powersave policy. Background HWP performance can be controlled by user space using sysfs interface for max/min frequency limits and energy performance preference settings. Based on workload characteristics these can be adjusted from user space. These limits are not changed dynamically by kernel based on workload. By default HWP defaults to energy performance preference value of 0x80 on majority of platforms(Scale is 0-255, 0 is max performance and 255 is min). This value offers best performance/watt and for majority of server workloads performance doesn't suffer. Also users always have option to use performance policy of intel_pstate, to get best performance. But user tend to run with out of box configuration, which is powersave policy on most of the distros. In some case it is possible to dynamically adjust performance, for example, when a CPU is woken up due to IO completion or thread migrate to a new CPU. In this case HWP algorithm will take some time to build utilization and ramp up P-states. So this may results in lower performance for some IO workloads and workloads which tend to migrate. The idea of this patch series is to temporarily boost performance dynamically in these cases. This is only applicable only when user is using powersave policy, not in performance policy. Results on a Skylake server: Benchmark Improvement % ---------------------------------------------------------------------- dbench 50.36 thread IO bench (tiobench) 10.35 File IO 9.81 sqlite 15.76 X264 -104 cores 9.75 Spec Power (Negligible impact 7382 Vs. 7378) Idle Power No change observed ----------------------------------------------------------------------- HWP brings in best performace/watt at EPP=0x80. Since we are boosting EPP here to 0, the performance/watt drops upto 10%. So there is a power penalty of these changes. Also Mel Gorman provided test results on a prior patchset, which shows benifits of this series. Srinivas Pandruvada (6): cpufreq: intel_pstate: Cache last HWP capability/request value cpufreq: intel_pstate: Add HWP boost utility functions cpufreq: intel_pstate: Add update_util_hook for HWP cpufreq: intel_pstate: HWP boost performance on IO wakeup cpufreq: intel_pstate: New sysfs entry to control HWP boost cpufreq: intel_pstate: enable boost for SKX drivers/cpufreq/intel_pstate.c | 183 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 179 insertions(+), 4 deletions(-) -- 2.13.6
