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    SubjectRe: [patch 00/18] CFS Bandwidth Control v7.2
    Hi Vladimir,

    I had a fairly good coversation with Pavel at LPC regarding these
    questions, it's probably worth syncing up with him and then following up
    if you still have questions.


    On 09/13/11 05:10, Vladimir Davydov wrote:
    > Hello, Paul
    >
    > I have a question about CFS bandwidth control.
    >
    > Let's consider a cgroup with several (>1) tasks running on a two CPU
    > host. Let the limit of the cgroup be 50% (e.g. period=1s, quota=0.5s).
    > How will tasks of the cgroup be distributed between the two CPUs? Will
    > they all run on one of the CPUs, or will one half of them run on one CPU
    > and others run on the other?
    >

    Parallelism is unconstrained until the bandwidth limit is reached, at
    which point we CONFIG_NR_CPUS=0

    > Although in both cases the tasks will consume not more than one half of
    > overall CPU time, the first case (all tasks of the cgroup run on the
    > same CPU) is obviously better if the tasks are likely to communicate
    > with each other (e.g. through pipe) which is often the case when cgroups
    > are used for container virtualization.
    >

    This case is handled already by the affine wake-up path.

    > In other words, I'd like to know if your code (or the scheduler code)
    > tries to gather all tasks of the same cgroup on such a subset of all
    > CPUs so that the tasks can't execute less CPUs without losing quota
    > during each period. And if not, are you going to address the issue?
    >

    Parallelism != Bandwidth; no plans at this time.

    Thanks!

    - Paul


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