• Paolo Valente's avatar
    block, bfq: don't change ioprio class for a bfq_queue on a service tree · 431b17f9
    Paolo Valente authored
    On each deactivation or re-scheduling (after being served) of a
    bfq_queue, BFQ invokes the function __bfq_entity_update_weight_prio(),
    to perform pending updates of ioprio, weight and ioprio class for the
    bfq_queue. BFQ also invokes this function on I/O-request dispatches,
    to raise or lower weights more quickly when needed, thereby improving
    latency. However, the entity representing the bfq_queue may be on the
    active (sub)tree of a service tree when this happens, and, although
    with a very low probability, the bfq_queue may happen to also have a
    pending change of its ioprio class. If both conditions hold when
    __bfq_entity_update_weight_prio() is invoked, then the entity moves to
    a sort of hybrid state: the new service tree for the entity, as
    returned by bfq_entity_service_tree(), differs from service tree on
    which the entity still is. The functions that handle activations and
    deactivations of entities do not cope with such a hybrid state (and
    would need to become more complex to cope).
    This commit addresses this issue by just making
    __bfq_entity_update_weight_prio() not perform also a possible pending
    change of ioprio class, when invoked on an I/O-request dispatch for a
    bfq_queue. Such a change is thus postponed to when
    __bfq_entity_update_weight_prio() is invoked on deactivation or
    re-scheduling of the bfq_queue.
    Reported-by: default avatarMarco Piazza <mpiazza@gmail.com>
    Reported-by: default avatarLaurentiu Nicola <lnicola@dend.ro>
    Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
    Tested-by: default avatarMarco Piazza <mpiazza@gmail.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
bfq-iosched.h 30.7 KB