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    SubjectRe: [PATCH] block: loop: avoiding too many pending per work I/O
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    Ming Lei <ming.lei@canonical.com> writes:

    > On Wed, Apr 29, 2015 at 12:36 AM, Jeff Moyer <jmoyer@redhat.com> wrote:
    >> Ming Lei <ming.lei@canonical.com> writes:
    >>
    >>> If there are too many pending per work I/O, too many
    >>> high priority work thread can be generated so that
    >>> system performance can be effected.
    >>>
    >>> This patch limits the max pending per work I/O as 16,
    >>> and will fackback to single queue mode when the max
    >>> number is reached.
    >>
    >> Actually, it limits it to 32. Also, there is no discussion on what
    >> variables might affect this number. Will that magic number change
    >> depending on the number of cpus on the system, for example?
    >
    > My fault, it should have been 16.
    >
    > It is just used to keep more IOs in flight, but can't cause obvious
    > costs like the case of Fedora live booting.
    >
    > IMO, it shouldn't depend much on number of CPUs, and more
    > related with I/O performance of the backing file, and the number
    > is like 'iodepth' of fio.

    OK, that makes more sense. I'm still not a huge fan of hard-coding
    numbers that are storage-specific, but I don't have a better suggestion
    at the moment, either.

    Cheers,
    Jeff


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