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    Subject[RFC/RFT] [PATCH 00/10] Intel_pstate: HWP Dynamic performance boost
    Date
    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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