• Davide Zini's avatar
    block, bfq: balance I/O injection among underutilized actuators · 1bd43e19
    Davide Zini authored
    Upon the invocation of its dispatch function, BFQ returns the next I/O
    request of the in-service bfq_queue, unless some exception holds. One
    such exception is that there is some underutilized actuator, different
    from the actuator for which the in-service queue contains I/O, and
    that some other bfq_queue happens to contain I/O for such an
    actuator. In this case, the next I/O request of the latter bfq_queue,
    and not of the in-service bfq_queue, is returned (I/O is injected from
    that bfq_queue). To find such an actuator, a linear scan, in
    increasing index order, is performed among actuators.
    
    Performing a linear scan entails a prioritization among actuators: an
    underutilized actuator may be considered for injection only if all
    actuators with a lower index are currently fully utilized, or if there
    is no pending I/O for any lower-index actuator that happens to be
    underutilized.
    
    This commits breaks this prioritization and tends to distribute
    injection uniformly across actuators. This is obtained by adding the
    following condition to the linear scan: even if an actuator A is
    underutilized, A is however skipped if its load is higher than that of
    the next actuator.
    Reviewed-by: default avatarDamien Le Moal <damien.lemoal@opensource.wdc.com>
    Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
    Signed-off-by: default avatarDavide Zini <davidezini2@gmail.com>
    Link: https://lore.kernel.org/r/20230103145503.71712-9-paolo.valente@linaro.orgSigned-off-by: default avatarJens Axboe <axboe@kernel.dk>
    1bd43e19
bfq-iosched.c 264 KB