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    Subject[PATCH 0/4] Optimize cgroup context switch
    Date
    From: Kan Liang <kan.liang@linux.intel.com>

    On systems with very high context switch rates between cgroups,
    there are high overhead using cgroup perf.

    Current codes have two issues.
    - System-wide events are mistakenly switched in cgroup
    context switch. It causes system-wide events miscounting,
    and brings avoidable overhead.
    Patch 1 fixes the issue.
    - The cgroup context switch sched_in is low efficient.
    All cgroup events share the same per-cpu pinned/flexible groups.
    The RB trees for pinned/flexible groups don't understand cgroup.
    Current code has to traverse all events, and use event_filter_match()
    to filter the events for specific cgroup.
    Patch 2-4 adds a fast path for cgroup context switch sched_in by
    training the RB tree to understand cgroup. The extra filtering
    can be avoided.


    Here is test with 6 cgroups running.
    Each cgroup has a specjbb benchmark running.
    The perf command is as below.
    perf stat -e cycles,instructions -e cycles,instructions
    -e cycles,instructions -e cycles,instructions
    -e cycles,instructions -e cycles,instructions
    -G cgroup1,cgroup1,cgroup2,cgroup2,cgroup3,cgroup3
    -G cgroup4,cgroup4,cgroup5,cgroup5,cgroup6,cgroup6
    -a -e cycles,instructions -I 1000

    The average RT (Response Time) reported from specjbb is
    used as key performance metrics. (The lower the better)

    RT(us) Overhead
    Baseline (no perf stat): 4286.9
    Use cgroup perf, no patches: 4483.6 4.6%
    Use cgroup perf, apply patch 1: 4369.2 1.9%
    Use cgroup perf, apple all patches: 4335.3 1.1%

    Kan Liang (4):
    perf: Fix system-wide events miscounting during cgroup monitoring
    perf: Add filter_match() as a parameter for pinned/flexible_sched_in()
    perf cgroup: Add cgroup ID as a key of RB tree
    perf cgroup: Add fast path for cgroup switch

    include/linux/perf_event.h | 7 ++
    kernel/events/core.c | 171 +++++++++++++++++++++++++++++++++++++++------
    2 files changed, 157 insertions(+), 21 deletions(-)

    --
    2.7.4

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