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    SubjectRe: [RFC PATCH] block: Fix bio merge induced high I/O latency
    On Mon, Jan 19 2009, Nikanth K wrote:
    > On Sun, Jan 18, 2009 at 12:34 AM, Jens Axboe <> wrote:
    > >
    > > As a quick test, could you try and increase the slice_idle to eg 20ms?
    > > Sometimes I've seen timing being slightly off, which makes us miss the
    > > sync window for the ls (in your case) process. Then you get a mix of
    > > async and sync IO all the time, which very much slows down the sync
    > > process.
    > >
    > Do you mean to say that 'ls' could not submit another request until
    > the previous sync request completes, but its idle window gets disabled
    > as it takes way too long to complete during heavy load? But when there

    'ls' would never submit a new request before the previous one completes,
    such is the nature of sync processes. That's the whole reason we have
    the idle window.

    > are requests in the driver, wont the idling be disabled anyway? Or did
    > you mean to increase slice_sync?

    No, idling is on a per-cfqq (process) basis. I did not mean to increase
    slice_sync, that wont help at all. It's the window between submissions
    of requests that I wanted to test being larger, but apparently that
    wasn't the case here.

    Jens Axboe

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      Last update: 2009-01-19 19:27    [W:0.020 / U:75.192 seconds]
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