Messages in this thread | | | From | Srinivas Pandruvada <> | Subject | [RFC/RFT] [PATCH 00/10] Intel_pstate: HWP Dynamic performance boost | Date | Tue, 15 May 2018 21:49:01 -0700 |
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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.
Peter Zijlstra (1): x86,sched: Add support for frequency invariance
Srinivas Pandruvada (9): cpufreq: intel_pstate: Conditional frequency invariant accounting cpufreq: intel_pstate: Utility functions to boost HWP performance limits cpufreq: intel_pstate: Add update_util_hook for HWP cpufreq: intel_pstate: HWP boost performance on IO Wake cpufreq / sched: Add interface to get utilization values cpufreq: intel_pstate: HWP boost performance on busy task migrate cpufreq: intel_pstate: Dyanmically update busy pct cpufreq: intel_pstate: New sysfs entry to control HWP boost cpufreq: intel_pstate: enable boost for SKX
arch/x86/include/asm/topology.h | 29 +++++ arch/x86/kernel/smpboot.c | 196 +++++++++++++++++++++++++++++- drivers/cpufreq/intel_pstate.c | 260 +++++++++++++++++++++++++++++++++++++++- include/linux/sched/cpufreq.h | 2 + kernel/sched/core.c | 1 + kernel/sched/cpufreq.c | 23 ++++ kernel/sched/sched.h | 7 ++ 7 files changed, 513 insertions(+), 5 deletions(-)
-- 2.9.5
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