lkml.org 
[lkml]   [2021]   [Sep]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.4 242/260] block, bfq: honor already-setup queue merges
    Date
    From: Paolo Valente <paolo.valente@linaro.org>

    [ Upstream commit 2d52c58b9c9bdae0ca3df6a1eab5745ab3f7d80b ]

    The function bfq_setup_merge prepares the merging between two
    bfq_queues, say bfqq and new_bfqq. To this goal, it assigns
    bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives,
    the process that generated that I/O is disassociated from bfqq and
    associated with new_bfqq (merging is actually a redirection). In this
    respect, bfq_setup_merge increases new_bfqq->ref in advance, adding
    the number of processes that are expected to be associated with
    new_bfqq.

    Unfortunately, the stable-merging mechanism interferes with this
    setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and
    before all the expected processes have been associated with
    bfqq->new_bfqq, bfqq may happen to be stably merged with a different
    queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq
    gets changed. So, some of the processes that have been already
    accounted for in the ref counter of the previous new_bfqq will not be
    associated with that queue. This creates an unbalance, because those
    references will never be decremented.

    This commit fixes this issue by reestablishing the previous, natural
    behaviour: once bfqq->new_bfqq has been set, it will not be changed
    until all expected redirections have occurred.

    Signed-off-by: Davide Zini <davidezini2@gmail.com>
    Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
    Link: https://lore.kernel.org/r/20210802141352.74353-2-paolo.valente@linaro.org
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    block/bfq-iosched.c | 16 +++++++++++++---
    1 file changed, 13 insertions(+), 3 deletions(-)

    diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
    index 73bffd7af15c..8dee243e639f 100644
    --- a/block/bfq-iosched.c
    +++ b/block/bfq-iosched.c
    @@ -2523,6 +2523,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
    * are likely to increase the throughput.
    */
    bfqq->new_bfqq = new_bfqq;
    + /*
    + * The above assignment schedules the following redirections:
    + * each time some I/O for bfqq arrives, the process that
    + * generated that I/O is disassociated from bfqq and
    + * associated with new_bfqq. Here we increases new_bfqq->ref
    + * in advance, adding the number of processes that are
    + * expected to be associated with new_bfqq as they happen to
    + * issue I/O.
    + */
    new_bfqq->ref += process_refs;
    return new_bfqq;
    }
    @@ -2582,6 +2591,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
    {
    struct bfq_queue *in_service_bfqq, *new_bfqq;

    + /* if a merge has already been setup, then proceed with that first */
    + if (bfqq->new_bfqq)
    + return bfqq->new_bfqq;
    +
    /*
    * Do not perform queue merging if the device is non
    * rotational and performs internal queueing. In fact, such a
    @@ -2636,9 +2649,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
    if (bfq_too_late_for_merging(bfqq))
    return NULL;

    - if (bfqq->new_bfqq)
    - return bfqq->new_bfqq;
    -
    if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
    return NULL;

    --
    2.30.2


    \
     
     \ /
      Last update: 2021-09-20 20:26    [W:4.252 / U:0.088 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site