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    SubjectRe: [RFC] CPU hard limits
    Bharata B Rao wrote:
    > On Fri, Jun 05, 2009 at 01:27:55PM +0800, Balbir Singh wrote:
    >
    >> * Avi Kivity <avi@redhat.com> [2009-06-05 08:21:43]:
    >>
    >>
    >>> Balbir Singh wrote:
    >>>
    >>>>> But then there is no other way to make a *guarantee*, guarantees come
    >>>>> at a cost of idling resources, no? Can you show me any other
    >>>>> combination that will provide the guarantee and without idling the
    >>>>> system for the specified guarantees?
    >>>>>
    >>>>>
    >>>> OK, I see part of your concern, but I think we could do some
    >>>> optimizations during design. For example if all groups have reached
    >>>> their hard-limit and the system is idle, should we do start a new hard
    >>>> limit interval and restart, so that idleness can be removed. Would
    >>>> that be an acceptable design point?
    >>>>
    >>> I think so. Given guarantees G1..Gn (0 <= Gi <= 1; sum(Gi) <= 1), and a
    >>> cpu hog running in each group, how would the algorithm divide resources?
    >>>
    >>>
    >> As per the matrix calculation, but as soon as we reach an idle point,
    >> we redistribute the b/w and start a new quantum so to speak, where all
    >> groups are charged up to their hard limits.
    >>
    >
    > But could there be client models where you are required to strictly
    > adhere to the limit within the bandwidth and not provide more (by advancing
    > the bandwidth period) in the presence of idle cycles ?
    >

    That's the limit part. I'd like to be able to specify limits and
    guarantees on the same host and for the same groups; I don't think that
    works when you advance the bandwidth period.

    I think we need to treat guarantees as first-class goals, not something
    derived from limits (in fact I think guarantees are more useful as they
    can be used to provide SLAs).

    --
    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.



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