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    SubjectRe: [RFC/RFT PATCH v3] sched: automated per tty task groups
    * Peter Zijlstra (peterz@infradead.org) wrote:
    > On Fri, 2010-11-19 at 12:49 +0100, Peter Zijlstra wrote:
    > > On Fri, 2010-11-19 at 00:43 +0100, Samuel Thibault wrote:
    > > > What overhead? The implementation of cgroups is actually already
    > > > hierarchical.
    > >
    > > It must be nice to be that ignorant ;-) Speaking for the scheduler
    > > cgroup controller (that being the only one I actually know), most all
    > > the load-balance operations are O(n) in the number of active cgroups,
    > > and a lot of the cpu local schedule operations are O(d) where d is the
    > > depth of the cgroup tree.
    > >
    > > [ and that's with the .38 targeted code, current mainline is O(n ln(n))
    > > for load balancing and truly sucks on multi-socket ]
    > >
    > > You add a lot of pointer chasing to all the scheduler fast paths and
    > > there is quite significant data size bloat for even compiling with the
    > > controller enabled, let alone actually using the stuff.
    > >
    > > But sure, treat them as if they were free to use, I guess your machine
    > > is fast enough.
    >
    > In general though, I think you can say that: cgroups ass overhead.

    I really think you meant "add" here ? (Hey! The keys were next to each other!)
    ;)

    > Simply because you add constraints, this means you need to 1) account
    > more, 2) enforce constraints. Both have definite non-zero cost in both
    > data and time.

    Yep, this looks like one of these perpetual throughput vs latency trade-offs.

    Thanks,

    Mathieu

    --
    Mathieu Desnoyers
    Operating System Efficiency R&D Consultant
    EfficiOS Inc.
    http://www.efficios.com


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