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    SubjectRe: Time sliced CFQ io scheduler
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    On Wed, 2004-12-08 at 03:51 +0100, Andrea Arcangeli wrote:
    > On Wed, Dec 08, 2004 at 01:33:33PM +1100, Nick Piggin wrote:
    > > I think we could detect when a disk asks for more than, say, 4
    > > concurrent requests, and in that case turn off read anticipation
    > > and all the anti-starvation for TCQ by default (with the option
    > > to force it back on).
    >
    > What do you mean with "disk asks for more than 4 concurrent requests?"
    > You mean checking the TCQ capability of the hardware storage?
    >

    Yeah. Just check if there are more than 4 outstanding requests at once.

    > > I think this would be a decent "it works" solution that would make
    > > AS acceptable as a default.
    >
    > Perhaps the code would be the same but if you disable it completely on
    > certain hardware that's not AS anymore...
    >

    Which is what we want on those system ;)

    > Then I believe it would be better to switch to cfq for storage capable
    > of more than 4 concurrent tagged queued requests instead of sticking
    > with a "disabled AS". What's the point of AS if the features of AS are
    > disabled?
    >

    For everyone else, who do want the AS features (ie. not databases).

    > One relevant feature of cfq is the fairness property of pid against pid
    > or user against user. You don't get that fairness with the other I/O
    > schedulers. It was designed for fairness since the first place. Fariness
    > of writes against writes and reads against reads and write against reads
    > and read against writes.

    That is something, I'll grant you that.


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