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    Subject[CFS Bandwidth Control v4 0/7] Introduction
    Hi all,

    Please find attached v4 of CFS bandwidth control; while this rebase against
    some of the latest SCHED_NORMAL code is new, the features and methodology are
    fairly mature at this point and have proved both effective and stable for
    several workloads.

    As always, all comments/feedback welcome.

    Changes since v3:
    - Rebased to current tip, update to work with new group scheduling accounting
    - (Bug fix) Fixed Race with unthrottling (due to changing global limit) fixed
    - (Bug fix) Fixed buddy interactions -- in particular, prevent buddy
    nominations from re-picking throttled entities

    The skeleton of our approach is as follows:
    - We maintain a global pool (per-tg) pool of unassigned quota. Within it
    we track the bandwidth period, quota per period, and runtime remaining in
    the current period. As bandwidth is used within a period it is decremented
    from runtime. Runtime is currently synchronized using a spinlock, in the
    current implementation there's no reason this couldn't be done using
    atomic ops instead however the spinlock allows for a little more flexibility
    in experimentation with other schemes.
    - When a cfs_rq participating in a bandwidth constrained task_group executes
    it acquires time in sysctl_sched_cfs_bandwidth_slice (default currently
    10ms) size chunks from the global pool, this synchronizes under rq->lock and
    is part of the update_curr path.
    - Throttled entities are dequeued, we protect against their re-introduction to
    the scheduling hierarchy via checking for a, per cfs_rq, throttled bit.

    Three new cgroupfs files are exported by the cpu subsystem:
    cpu.cfs_period_us : period over which bandwidth is to be regulated
    cpu.cfs_quota_us : bandwidth available for consumption per period
    cpu.stat : statistics (such as number of throttled periods and
    total throttled time)
    One important interface change that this introduces (versus the rate limits
    proposal) is that the defined bandwidth becomes an absolute quantifier.

    Previous postings:
    Original posting:

    Prior approaches: ("CFS Hard limits v5")


    - Paul

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