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    SubjectRe: [PATCH 1/7] CPU controller V1 - split runqueue
    On Fri, Aug 25, 2006 at 04:38:00PM +0400, Kirill Korotaev wrote:
    > Srivatsa,
    >
    > I suggest to split existing runqueue structure
    > into 2 pieces: physical cpu (sd, ...) and
    > virtual cpu (essentially a runqueue - array, nr_running, loac etc.)
    >
    > Then replace all references to cpu as int with vcpu_t pointer.

    That's going to be a massive change! If I understand you correctly,
    things like get_cpu() return virtual CPU number rather than the
    corresponding "physical" CPU (the later is anyway a misnomer on
    virtualized platforms)? Also we have get_cpu() now reading some structure and be
    able to tell which CPU a task is running. Now with virtual CPUs, another
    level of translation is needed? Wonder what the performance impact of
    that would be ..

    > What advantages does it give?
    > 1. it isolates Linux std scheduler code for scheduling
    > tasks inside runqueues, while adds possibility
    > to add cleanly more high-level scheduler, which can select
    > runqueues to run (lets call it "process groups scheduler" - PGS).
    > 2. runqueues can run on arbitrary physical CPUs if needed
    > which helps to solve balancing problem on SMP.

    How do you see the relation between load-balance done thr sched-domain
    heirarchy today and what will be done thr' virtal runqueues?

    > 3. it allows naturally to use different PGS algorithms
    > on top of Linux one. e.g. yours algorithm (probobalistic) or
    > fair scheduling algorithms like SFQ, EEVDF, BVT with more
    > predictable parameters of QoS.
    > 4. it will help us to get to the consensus and commit this work
    > into mainstream, because different PGS with different properties
    > will be possible.
    >
    > Part of this idea is implemented in OpenVZ scheduler and in some
    > regards looks very much like your work, so I think if you like the idea
    > we can eloborate.
    >
    > What do you think?

    I believe hypervisors like Xen have a similar approach (virtualing CPU
    resource and running a virtual CPU on any available physical CPU). The
    worry I have applying this to Linux kernel scheduler is in terms of its
    invasiveness and thus general acceptability. I will however let the maintainers
    decide on that. Sending some patches also probably will help measure this
    "invasiveness/acceptability".

    I had another question related to real-time tasks. How do you control
    CPU usage of real-time tasks in different containers (especially if they
    are SCHED_FIFO types)? Do they get capped at the bandwidth provided to
    the container?

    Also do you take any special steps to retain interactivity?

    --
    Regards,
    vatsa
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