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    SubjectRe: [PATCH] cfq-iosched: don't allow aliased requests to starve others
    On 2010-07-26 15:17, Jeff Moyer wrote:
    > Jens Axboe <axboe@kernel.dk> writes:
    >
    >> On 07/24/2010 10:04 AM, Heinz Diehl wrote:
    >>> On 14.07.2010, Jeff Moyer wrote:
    >>>
    >>>> Comments, as always, are welcome.
    >>>
    >>> This patch, applied to 2.6.35-rc6, increases desktop interactivity
    >>> _NOTICEABLY_ on my quadcore machine, and the machine stays rock-stable.
    >>> I have now tested this patch with the latest 2.6.35-rc kernels over
    >>> 1 week.
    >>>
    >>> Unfortunately, I can't provide some testing results which makes this
    >>> statement more objective, but I'll do some synthetic testing in the next
    >>> days.
    >>
    >> It is extremely unlikely that this patch will have any impact on
    >> "normal" workloads. To even hit a code path where it would make a
    >> difference, you would need to use O_DIRECT IO, otherwise you cannot have
    >> aliases in the IO scheduler.
    >
    > I agree that it shouldn't help normal workloads at all. I do think
    > there is one other case where you can get aliases: doing I/O both
    > through the file system and the underlying device. However, that's
    > obviously a bad idea (and maybe open_bdev_exclusive will keep that from
    > happening?).

    That's correct, you could construct such a test case since you would
    get page cache synchronization from different mappings. But again,
    not something that the casual user would run into :-)

    Exclusive opens only guard against each other, not against "normal"
    opens.

    --
    Jens Axboe



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