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    SubjectRe: [RFC 0/5] sched: Add CPU rate caps
    Con Kolivas wrote:
    > On Friday 26 May 2006 14:20, Peter Williams wrote:
    >> These patches implement CPU usage rate limits for tasks.
    >> Although the rlimit mechanism already has a CPU usage limit (RLIMIT_CPU)
    >> it is a total usage limit and therefore (to my mind) not very useful.
    >> These patches provide an alternative whereby the (recent) average CPU
    >> usage rate of a task can be limited to a (per task) specified proportion
    >> of a single CPU's capacity. The limits are specified in parts per
    >> thousand and come in two varieties -- hard and soft. The difference
    >> between the two is that the system tries to enforce hard caps regardless
    >> of the other demand for CPU resources but allows soft caps to be
    >> exceeded if there are spare CPU resources available. By default, tasks
    >> will have both caps set to 1000 (i.e. no limit) but newly forked tasks
    >> will inherit any caps that have been imposed on their parent from the
    >> parent. The mimimim soft cap allowed is 0 (which effectively puts the
    >> task in the background) and the minimim hard cap allowed is 1.
    >> Care has been taken to minimize the overhead inflicted on tasks that
    >> have no caps and my tests using kernbench indicate that it is hidden in
    >> the noise.
    > The presence of tasks with caps will break smp balancing and smp nice. I
    > suspect you could probably provide a reasonable workaround by altering their
    > priority bias effect in the raw weighted load in smp nice for soft caps by
    > the percentage cpu of the cap. Hard caps provide more "interesting"
    > challenges though. I can't think of a valid biasing off hand for them, but at
    > least initially using the same logic as soft caps should help.

    I thought that I already did that? Check the changes to set_load_weight().

    Peter Williams

    "Learning, n. The kind of ignorance distinguishing the studious."
    -- Ambrose Bierce
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