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    SubjectRe: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
    Date
    On 2019/11/08 4:00, Andrea Vai wrote:
    > [Sorry for the duplicate message, it didn't reach the lists due to
    > html formatting]
    > Il giorno gio 7 nov 2019 alle ore 08:54 Damien Le Moal
    > <Damien.LeMoal@wdc.com> ha scritto:
    >>
    >> On 2019/11/07 16:04, Andrea Vai wrote:
    >>> Il giorno mer, 06/11/2019 alle 22.13 +0000, Damien Le Moal ha scritto:
    >>>>
    >>>>
    >>>> Please simply try your write tests after doing this:
    >>>>
    >>>> echo mq-deadline > /sys/block/<name of your USB
    >>>> disk>/queue/scheduler
    >>>>
    >>>> And confirm that mq-deadline is selected with:
    >>>>
    >>>> cat /sys/block/<name of your USB disk>/queue/scheduler
    >>>> [mq-deadline] kyber bfq none
    >>>
    >>> ok, which kernel should I test with this: the fresh git cloned, or the
    >>> one just patched with Alan's patch, or doesn't matter which one?
    >>
    >> Probably all of them to see if there are any differences.
    >
    > with both kernels, the output of
    > cat /sys/block/sdh/queue/schedule
    >
    > already contains [mq-deadline]: is it correct to assume that the echo
    > command and the subsequent testing is useless? What to do now?

    Probably, yes. Have you obtained a blktrace of the workload during these
    tests ? Any significant difference in the IO pattern (IO size and
    randomness) and IO timing (any device idle time where the device has no
    command to process) ? Asking because the problem may be above the block
    layer, with the file system for instance.

    >
    > Thanks, and bye
    > Andrea
    >


    --
    Damien Le Moal
    Western Digital Research

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