lkml.org 
[lkml]   [2009]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC] CPU hard limits
    Balbir Singh wrote:
    > On Fri, Jun 5, 2009 at 11:33 AM, Avi Kivity <avi@redhat.com> wrote:
    >
    >> Bharata B Rao wrote:
    >>
    >>>> Another way is to place the 8 groups in a container group, and limit
    >>>> that to 80%. But that doesn't work if I want to provide guarantees to
    >>>> several groups.
    >>>>
    >>>>
    >>> Hmm why not ? Reduce the guarantee of the container group and provide
    >>> the same to additional groups ?
    >>>
    >>>
    >> This method produces suboptimal results:
    >>
    >> $ cgroup-limits 10 10 0
    >> [50.0, 50.0, 40.0]
    >>
    >> I want to provide two 10% guaranteed groups and one best-effort group.
    >> Using the limits method, no group can now use more than 50% of the
    >> resources. However, having the first group use 90% of the resources does
    >> not violate any guarantees, but it not allowed by the solution.
    >>
    >>
    >
    > How, it works out fine in my calculation
    >
    > 50 + 40 for G2 and G3, make sure that G1 gets 10%, since others are
    > limited to 90%
    > 50 + 40 for G1 and G3, make sure that G2 gets 10%, since others are
    > limited to 90%
    > 50 + 50 for G1 and G2, make sure that G3 gets 0%, since others are
    > limited to 100%
    >

    It's fine in that it satisfies the guarantees, but it is deeply
    suboptimal. If I ran a cpu hog in the first group, while the other two
    were idle, it would be limited to 50% cpu. On the other hand, if it
    consumed all 100% cpu it would still satisfy the guarantees (as the
    other groups are idle).

    The result is that in such a situation, wall clock time would double
    even though cpu resources are available.
    > Now if we really have zeros, I would recommend using
    >
    > cgroup-limits 10 10 and you'll see that you'll get 90, 90 as output.
    >
    > Adding zeros to the calcuation is not recommended. Does that help?

    What do you mean, it is not recommended? I have two groups which need at
    least 10% and one which does not need any guarantee, how do I express it?

    In any case, changing the zero to 1% does not materially change the results.

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



    \
     
     \ /
      Last update: 2009-06-05 06:49    [W:0.023 / U:2.336 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site