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    SubjectRe: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
    David Lang <> wrote:
    > note that issuing a fsync should change all pending writes to 'syncronous'
    > as should writes to any partition mounted with the sync option, or writes
    > to a directory with the S flag set.

    We know, at I/O submission time, whether a write is to be waited upon.
    That's in writeback_control.sync_mode.

    That, combined with an assumption that "all reads are synchronous" would
    allow the outgoing BIOs to be appropriately tagged.

    It's still approximate. An exact solution would involve only marking I/O as
    synchronous when some process actually waits on its completion. I do not
    believe that all the extra lookup and locking infrastructure and storage
    which this would require is justified. Certainly not in a first iteration.

    The Rice Uni researchers did implement controls which attempted to learn IO
    submission patterns on a per-process basis, and I believe these were also
    used to avoid undesirable starvations. We have only briefly played with
    process-aware logic.

    The first thing to do is to get the anticipatory scheduler working properly.
    Nick has been tied down for a week chasing generic bugs in the request layer.
    He seems to have nailed the important ones now.

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      Last update: 2005-03-22 13:33    [W:0.020 / U:4.572 seconds]
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