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    SubjectRe: [RFC 0/2] optimise local-tw task resheduling
    Hi Pavel

    On Fri, Mar 10, 2023 at 07:04:14PM +0000, Pavel Begunkov wrote:
    > io_uring extensively uses task_work, but when a task is waiting
    > for multiple CQEs it causes lots of rescheduling. This series
    > is an attempt to optimise it and be a base for future improvements.
    >
    > For some zc network tests eventually waiting for a portion of
    > buffers I've got 10x descrease in the number of context switches,
    > which reduced the CPU consumption more than twice (17% -> 8%).
    > It also helps storage cases, while running fio/t/io_uring against
    > a low performant drive it got 2x descrease of the number of context
    > switches for QD8 and ~4 times for QD32.

    ublk uses io_uring_cmd_complete_in_task()(io_req_task_work_add())
    heavily. So I tried this patchset, looks not see obvious change
    on both IOPS and context switches when running 't/io_uring /dev/ublkb0',
    and it is one null ublk target(ublk add -t null -z -u 1 -q 2), IOPS
    is ~2.8M.

    But ublk applies batch schedule similar with io_uring before calling
    io_uring_cmd_complete_in_task().

    thanks,
    Ming

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