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    SubjectRe: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
    On Mon, Feb 10, 2003 at 03:58:26PM +1100, Nick Piggin wrote:
    ...
    > >If we assume they are synchronous, that would be rather unfair
    > >especially on multi-user systems - and the 90% accuracy that Rik
    > >suggested would seem exaggerated to say the least (accuracy would be
    > >more like 10% on a good day).
    > >
    > Remember that readahead gets scaled down quickly if it isn't
    > getting hits. It is also likely to be sequential and in the
    > track buffer, so it is a small cost.

    I buy the sequential-argument - very good point.

    Thanks,

    > Huge readahead is a problem however anticipatory scheduling
    > will hopefully allow good throughput for multiple read streams
    > without requiring much readahead.

    I'm curious as to how these things will interact in the NFS
    server<->client situation :)

    Time will show, I guess.

    Random data-point (not meant as a rant - I'm happy for all I got ;)

    In stock 2.4.20 the interaction is horrible - whatever was done there is
    not optimal. A 'tar xf' on the client will neither load the network
    nor the server - it seems to be network latency bound (readahead not
    doing it's job - changing min-readahead and max-readahead on the client
    doesn't seem to make a difference). However, my desktop (running on the
    client) can hang for 10 seconds straight every half hour or so, when the
    nightly backup runs on the server (local disk reads streaming at around
    2 MB/sec from an array capable of at least 40 MB/sec).

    --
    ................................................................
    : jakob@unthought.net : And I see the elder races, :
    :.........................: putrid forms of man :
    : Jakob Østergaard : See him rise and claim the earth, :
    : OZ9ABN : his downfall is at hand. :
    :.........................:............{Konkhra}...............:
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