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    SubjectRe: [PATCH v2 14/14] Change CPUACCT to default n
    On Thu, Nov 24, 2011 at 6:05 PM, Li Zefan <lizf@cn.fujitsu.com> wrote:
    >> despite it being a not entirely natural fit.  Something I proposed at
    >> Prague and that we could explore here is the idea of a co-mounted
    >> controller.  In this example it would only be mountable with cpu so
    >> you could always depend on the cpu hierarchy being there; likewise we
    >> can put (jump-labeled) touchpoints within the cpu-subsystem to call
    >> out for updates as appropriate when the co-mount exists.
    >>
    >
    > IIUC, this co-mounting idea is something I implemented years ago:
    >
    > https://lkml.org/lkml/2008/6/18/389
    >
    > The use case and the reason it was rejected:
    >
    > https://lkml.org/lkml/2008/7/1/97
    >

    Rejection is a bit of a strong statement -- the idea seemed amenable
    but lacking a strong use-case. That said, taking a deep look at some
    of what Glauber is trying to do in this series I don't think it's
    something that would help here.

    For this discussion the motivation for a co-mount would be to
    piggy-back on the cpu sub-systems own hierarchy walks to reduce
    overhead. However, this is not structured in a way that can take
    advantage of this, and, looking at what Glauber is attempting to
    collect it's not clear that it can be.

    I think this moves the discussion towards whether we should consider
    deprecating some of the exported fields (namely usage and
    usage_per_cpu) from cpuacct instead of the entire controller as we had
    initially desired. This would allow cpuacct to exist with a much
    lower overhead, especially within the context-switch path.

    - Paul

    > --
    > Li Zefan
    >
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