releases/4.19.34/block-bfq-fix-in-service-queue-check-for-queue-mergi.patch

   1 From 14a5279754eea932b7719e108e8c0835f6aa2a54 Mon Sep 17 00:00:00 2001
   2 From: Paolo Valente <paolo.valente@linaro.org>
   3 Date: Tue, 29 Jan 2019 12:06:38 +0100
   4 Subject: block, bfq: fix in-service-queue check for queue merging
   5
   6 [ Upstream commit 058fdecc6de7cdecbf4c59b851e80eb2d6c5295f ]
   7
   8 When a new I/O request arrives for a bfq_queue, say Q, bfq checks
   9 whether that request is close to
  10 (a) the head request of some other queue waiting to be served, or
  11 (b) the last request dispatched for the in-service queue (in case Q
  12 itself is not the in-service queue)
  13
  14 If a queue, say Q2, is found for which the above condition holds, then
  15 bfq merges Q and Q2, to hopefully get a more sequential I/O in the
  16 resulting merged queue, and thus a possibly higher throughput.
  17
  18 Case (b) is checked by comparing the new request for Q with the last
  19 request dispatched, assuming that the latter necessarily belonged to the
  20 in-service queue. Unfortunately, this assumption is no longer always
  21 correct, since commit d0edc2473be9 ("block, bfq: inject other-queue I/O
  22 into seeky idle queues on NCQ flash").
  23
  24 When the assumption does not hold, queues that must not be merged may be
  25 merged, causing unexpected loss of control on per-queue service
  26 guarantees.
  27
  28 This commit solves this problem by adding an extra field, which stores
  29 the actual last request dispatched for the in-service queue, and by
  30 using this new field to correctly check case (b).
  31
  32 Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
  33 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  34 Signed-off-by: Sasha Levin <sashal@kernel.org>
  35 ---
  36  block/bfq-iosched.c | 5 ++++-
  37  block/bfq-iosched.h | 3 +++
  38  2 files changed, 7 insertions(+), 1 deletion(-)
  39
  40 diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
  41 index 653100fb719e..c5e2c5a01182 100644
  42 --- a/block/bfq-iosched.c
  43 +++ b/block/bfq-iosched.c
  44 @@ -2215,7 +2215,8 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
  45
  46         if (in_service_bfqq && in_service_bfqq != bfqq &&
  47             likely(in_service_bfqq != &bfqd->oom_bfqq) &&
  48 -           bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) &&
  49 +           bfq_rq_close_to_sector(io_struct, request,
  50 +                                  bfqd->in_serv_last_pos) &&
  51             bfqq->entity.parent == in_service_bfqq->entity.parent &&
  52             bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
  53                 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
  54 @@ -2755,6 +2756,8 @@ update_rate_and_reset:
  55         bfq_update_rate_reset(bfqd, rq);
  56  update_last_values:
  57         bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
  58 +       if (RQ_BFQQ(rq) == bfqd->in_service_queue)
  59 +               bfqd->in_serv_last_pos = bfqd->last_position;
  60         bfqd->last_dispatch = now_ns;
  61  }
  62
  63 diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
  64 index a8a2e5aca4d4..d5e9e60cb1a5 100644
  65 --- a/block/bfq-iosched.h
  66 +++ b/block/bfq-iosched.h
  67 @@ -469,6 +469,9 @@ struct bfq_data {
  68         /* on-disk position of the last served request */
  69         sector_t last_position;
  70
  71 +       /* position of the last served request for the in-service queue */
  72 +       sector_t in_serv_last_pos;
  73 +
  74         /* time of last request completion (ns) */
  75         u64 last_completion;
  76
  77 --
  78 2.19.1
  79