1. 17 Dec, 2018 2 commits
    • Ming Lei's avatar
      blk-mq: fix dispatch from sw queue · c16d6b5a
      Ming Lei authored
      When a request is added to rq list of sw queue(ctx), the rq may be from
      a different type of hctx, especially after multi queue mapping is
      introduced.
      
      So when dispach request from sw queue via blk_mq_flush_busy_ctxs() or
      blk_mq_dequeue_from_ctx(), one request belonging to other queue type of
      hctx can be dispatched to current hctx in case that read queue or poll
      queue is enabled.
      
      This patch fixes this issue by introducing per-queue-type list.
      
      Cc: Christoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      
      Changed by me to not use separately cacheline aligned lists, just
      place them all in the same cacheline where we had just the one list
      and lock before.
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      c16d6b5a
    • Christoph Hellwig's avatar
      blk-mq: only dispatch to non-defauly queue maps if they have queues · 5aceaeb2
      Christoph Hellwig authored
      We should check if a given queue map actually has queues enabled before
      dispatching to it.  This allows drivers to not initialize optional but
      not used map types, which subsequently will allow fixing problems with
      queue map rebuilds for that case.
      Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      5aceaeb2
  2. 16 Dec, 2018 1 commit
  3. 10 Dec, 2018 1 commit
  4. 04 Dec, 2018 1 commit
  5. 29 Nov, 2018 1 commit
  6. 21 Nov, 2018 1 commit
  7. 07 Nov, 2018 7 commits
  8. 17 Jul, 2018 1 commit
    • Ming Lei's avatar
      blk-mq: issue directly if hw queue isn't busy in case of 'none' · 6ce3dd6e
      Ming Lei authored
      In case of 'none' io scheduler, when hw queue isn't busy, it isn't
      necessary to enqueue request to sw queue and dequeue it from
      sw queue because request may be submitted to hw queue asap without
      extra cost, meantime there shouldn't be much request in sw queue,
      and we don't need to worry about effect on IO merge.
      
      There are still some single hw queue SCSI HBAs(HPSA, megaraid_sas, ...)
      which may connect high performance devices, so 'none' is often required
      for obtaining good performance.
      
      This patch improves IOPS and decreases CPU unilization on megaraid_sas,
      per Kashyap's test.
      
      Cc: Kashyap Desai <kashyap.desai@broadcom.com>
      Cc: Laurence Oberman <loberman@redhat.com>
      Cc: Omar Sandoval <osandov@fb.com>
      Cc: Christoph Hellwig <hch@lst.de>
      Cc: Bart Van Assche <bart.vanassche@wdc.com>
      Cc: Hannes Reinecke <hare@suse.de>
      Reported-by: default avatarKashyap Desai <kashyap.desai@broadcom.com>
      Tested-by: default avatarKashyap Desai <kashyap.desai@broadcom.com>
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      6ce3dd6e
  9. 09 Jul, 2018 2 commits
  10. 29 May, 2018 1 commit
    • Keith Busch's avatar
      blk-mq: Remove generation seqeunce · 12f5b931
      Keith Busch authored
      This patch simplifies the timeout handling by relying on the request
      reference counting to ensure the iterator is operating on an inflight
      and truly timed out request. Since the reference counting prevents the
      tag from being reallocated, the block layer no longer needs to prevent
      drivers from completing their requests while the timeout handler is
      operating on it: a driver completing a request is allowed to proceed to
      the next state without additional syncronization with the block layer.
      
      This also removes any need for generation sequence numbers since the
      request lifetime is prevented from being reallocated as a new sequence
      while timeout handling is operating on it.
      
      To enables this a refcount is added to struct request so that request
      users can be sure they're operating on the same request without it
      changing while they're processing it.  The request's tag won't be
      released for reuse until both the timeout handler and the completion
      are done with it.
      Signed-off-by: default avatarKeith Busch <keith.busch@intel.com>
      [hch: slight cleanups, added back submission side hctx lock, use cmpxchg
       for completions]
      Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      12f5b931
  11. 26 Apr, 2018 1 commit
  12. 25 Apr, 2018 1 commit
  13. 11 Apr, 2018 1 commit
    • Ming Lei's avatar
      blk-mq: Revert "blk-mq: reimplement blk_mq_hw_queue_mapped" · 2434af79
      Ming Lei authored
      This reverts commit 127276c6.
      
      When all CPUs of one hw queue become offline, there still may have IOs
      not completed from this hctx. But blk_mq_hw_queue_mapped() is called in
      blk_mq_queue_tag_busy_iter(), which is used for iterating request in timeout
      handler, timeout event will be missed on the inactive hctx, then request may
      never be completed.
      
      Also the replementation of blk_mq_hw_queue_mapped() doesn't match the helper's
      name any more, and it should have been named as blk_mq_hw_queue_active().
      
      Even other callers need further verification about this reimplemenation.
      
      So revert this patch now, and we can improve hw queue activate/inactivate event
      after adequent researching and test.
      
      Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
      Cc: Christian Borntraeger <borntraeger@de.ibm.com>
      Cc: Christoph Hellwig <hch@lst.de>
      Reported-by: default avatarJens Axboe <axboe@kernel.dk>
      Fixes: 	127276c6 ("blk-mq: reimplement blk_mq_hw_queue_mapped")
      Reviewed-by: default avatarSagi Grimberg <sagi@grimberg.me>
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      2434af79
  14. 10 Apr, 2018 1 commit
  15. 19 Jan, 2018 1 commit
  16. 17 Jan, 2018 1 commit
    • Ming Lei's avatar
      blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback · 396eaf21
      Ming Lei authored
      blk_insert_cloned_request() is called in the fast path of a dm-rq driver
      (e.g. blk-mq request-based DM mpath).  blk_insert_cloned_request() uses
      blk_mq_request_bypass_insert() to directly append the request to the
      blk-mq hctx->dispatch_list of the underlying queue.
      
      1) This way isn't efficient enough because the hctx spinlock is always
      used.
      
      2) With blk_insert_cloned_request(), we completely bypass underlying
      queue's elevator and depend on the upper-level dm-rq driver's elevator
      to schedule IO.  But dm-rq currently can't get the underlying queue's
      dispatch feedback at all.  Without knowing whether a request was issued
      or not (e.g. due to underlying queue being busy) the dm-rq elevator will
      not be able to provide effective IO merging (as a side-effect of dm-rq
      currently blindly destaging a request from its elevator only to requeue
      it after a delay, which kills any opportunity for merging).  This
      obviously causes very bad sequential IO performance.
      
      Fix this by updating blk_insert_cloned_request() to use
      blk_mq_request_direct_issue().  blk_mq_request_direct_issue() allows a
      request to be issued directly to the underlying queue and returns the
      dispatch feedback (blk_status_t).  If blk_mq_request_direct_issue()
      returns BLK_SYS_RESOURCE the dm-rq driver will now use DM_MAPIO_REQUEUE
      to _not_ destage the request.  Whereby preserving the opportunity to
      merge IO.
      
      With this, request-based DM's blk-mq sequential IO performance is vastly
      improved (as much as 3X in mpath/virtio-scsi testing).
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      [blk-mq.c changes heavily influenced by Ming Lei's initial solution, but
      they were refactored to make them less fragile and easier to read/review]
      Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      396eaf21
  17. 09 Jan, 2018 3 commits
    • Tejun Heo's avatar
      blk-mq: remove REQ_ATOM_STARTED · 5a61c363
      Tejun Heo authored
      After the recent updates to use generation number and state based
      synchronization, we can easily replace REQ_ATOM_STARTED usages by
      adding an extra state to distinguish completed but not yet freed
      state.
      
      Add MQ_RQ_COMPLETE and replace REQ_ATOM_STARTED usages with
      blk_mq_rq_state() tests.  REQ_ATOM_STARTED no longer has any users
      left and is removed.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      5a61c363
    • Tejun Heo's avatar
      blk-mq: make blk_abort_request() trigger timeout path · 358f70da
      Tejun Heo authored
      With issue/complete and timeout paths now using the generation number
      and state based synchronization, blk_abort_request() is the only one
      which depends on REQ_ATOM_COMPLETE for arbitrating completion.
      
      There's no reason for blk_abort_request() to be a completely separate
      path.  This patch makes blk_abort_request() piggyback on the timeout
      path instead of trying to terminate the request directly.
      
      This removes the last dependency on REQ_ATOM_COMPLETE in blk-mq.
      
      Note that this makes blk_abort_request() asynchronous - it initiates
      abortion but the actual termination will happen after a short while,
      even when the caller owns the request.  AFAICS, SCSI and ATA should be
      fine with that and I think mtip32xx and dasd should be safe but not
      completely sure.  It'd be great if people who know the drivers take a
      look.
      
      v2: - Add comment explaining the lack of synchronization around
            ->deadline update as requested by Bart.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Cc: Asai Thambi SP <asamymuthupa@micron.com>
      Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
      Cc: Jan Hoeppner <hoeppner@linux.vnet.ibm.com>
      Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      358f70da
    • Tejun Heo's avatar
      blk-mq: replace timeout synchronization with a RCU and generation based scheme · 1d9bd516
      Tejun Heo authored
      Currently, blk-mq timeout path synchronizes against the usual
      issue/completion path using a complex scheme involving atomic
      bitflags, REQ_ATOM_*, memory barriers and subtle memory coherence
      rules.  Unfortunately, it contains quite a few holes.
      
      There's a complex dancing around REQ_ATOM_STARTED and
      REQ_ATOM_COMPLETE between issue/completion and timeout paths; however,
      they don't have a synchronization point across request recycle
      instances and it isn't clear what the barriers add.
      blk_mq_check_expired() can easily read STARTED from N-2'th iteration,
      deadline from N-1'th, blk_mark_rq_complete() against Nth instance.
      
      In fact, it's pretty easy to make blk_mq_check_expired() terminate a
      later instance of a request.  If we induce 5 sec delay before
      time_after_eq() test in blk_mq_check_expired(), shorten the timeout to
      2s, and issue back-to-back large IOs, blk-mq starts timing out
      requests spuriously pretty quickly.  Nothing actually timed out.  It
      just made the call on a recycle instance of a request and then
      terminated a later instance long after the original instance finished.
      The scenario isn't theoretical either.
      
      This patch replaces the broken synchronization mechanism with a RCU
      and generation number based one.
      
      1. Each request has a u64 generation + state value, which can be
         updated only by the request owner.  Whenever a request becomes
         in-flight, the generation number gets bumped up too.  This provides
         the basis for the timeout path to distinguish different recycle
         instances of the request.
      
         Also, marking a request in-flight and setting its deadline are
         protected with a seqcount so that the timeout path can fetch both
         values coherently.
      
      2. The timeout path fetches the generation, state and deadline.  If
         the verdict is timeout, it records the generation into a dedicated
         request abortion field and does RCU wait.
      
      3. The completion path is also protected by RCU (from the previous
         patch) and checks whether the current generation number and state
         match the abortion field.  If so, it skips completion.
      
      4. The timeout path, after RCU wait, scans requests again and
         terminates the ones whose generation and state still match the ones
         requested for abortion.
      
         By now, the timeout path knows that either the generation number
         and state changed if it lost the race or the completion will yield
         to it and can safely timeout the request.
      
      While it's more lines of code, it's conceptually simpler, doesn't
      depend on direct use of subtle memory ordering or coherence, and
      hopefully doesn't terminate the wrong instance.
      
      While this change makes REQ_ATOM_COMPLETE synchronization unnecessary
      between issue/complete and timeout paths, REQ_ATOM_COMPLETE isn't
      removed yet as it's still used in other places.  Future patches will
      move all state tracking to the new mechanism and remove all bitops in
      the hot paths.
      
      Note that this patch adds a comment explaining a race condition in
      BLK_EH_RESET_TIMER path.  The race has always been there and this
      patch doesn't change it.  It's just documenting the existing race.
      
      v2: - Fixed BLK_EH_RESET_TIMER handling as pointed out by Jianchao.
          - s/request->gstate_seqc/request->gstate_seq/ as suggested by Peter.
          - READ_ONCE() added in blk_mq_rq_update_state() as suggested by Peter.
      
      v3: - Fixed possible extended seqcount / u64_stats_sync read looping
            spotted by Peter.
          - MQ_RQ_IDLE was incorrectly being set in complete_request instead
            of free_request.  Fixed.
      
      v4: - Rebased on top of hctx_lock() refactoring patch.
          - Added comment explaining the use of hctx_lock() in completion path.
      
      v5: - Added comments requested by Bart.
          - Note the addition of BLK_EH_RESET_TIMER race condition in the
            commit message.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Christoph Hellwig <hch@lst.de>
      Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      1d9bd516
  18. 11 Nov, 2017 2 commits
    • Jens Axboe's avatar
      blk-mq: only run the hardware queue if IO is pending · 79f720a7
      Jens Axboe authored
      Currently we are inconsistent in when we decide to run the queue. Using
      blk_mq_run_hw_queues() we check if the hctx has pending IO before
      running it, but we don't do that from the individual queue run function,
      blk_mq_run_hw_queue(). This results in a lot of extra and pointless
      queue runs, potentially, on flush requests and (much worse) on tag
      starvation situations. This is observable just looking at top output,
      with lots of kworkers active. For the !async runs, it just adds to the
      CPU overhead of blk-mq.
      
      Move the has-pending check into the run function instead of having
      callers do it.
      Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      79f720a7
    • Bart Van Assche's avatar
      block, nvme: Introduce blk_mq_req_flags_t · 9a95e4ef
      Bart Van Assche authored
      Several block layer and NVMe core functions accept a combination
      of BLK_MQ_REQ_* flags through the 'flags' argument but there is
      no verification at compile time whether the right type of block
      layer flags is passed. Make it possible for sparse to verify this.
      This patch does not change any functionality.
      Signed-off-by: default avatarBart Van Assche <bart.vanassche@wdc.com>
      Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
      Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
      Cc: linux-nvme@lists.infradead.org
      Cc: Christoph Hellwig <hch@lst.de>
      Cc: Johannes Thumshirn <jthumshirn@suse.de>
      Cc: Ming Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      9a95e4ef
  19. 04 Nov, 2017 3 commits
  20. 02 Nov, 2017 1 commit
    • Greg Kroah-Hartman's avatar
      License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
      Greg Kroah-Hartman authored
      Many source files in the tree are missing licensing information, which
      makes it harder for compliance tools to determine the correct license.
      
      By default all files without license information are under the default
      license of the kernel, which is GPL version 2.
      
      Update the files which contain no license information with the 'GPL-2.0'
      SPDX license identifier.  The SPDX identifier is a legally binding
      shorthand, which can be used instead of the full boiler plate text.
      
      This patch is based on work done by Thomas Gleixner and Kate Stewart and
      Philippe Ombredanne.
      
      How this work was done:
      
      Patches were generated and checked against linux-4.14-rc6 for a subset of
      the use cases:
       - file had no licensing information it it.
       - file was a */uapi/* one with no licensing information in it,
       - file was a */uapi/* one with existing licensing information,
      
      Further patches will be generated in subsequent months to fix up cases
      where non-standard license headers were used, and references to license
      had to be inferred by heuristics based on keywords.
      
      The analysis to determine which SPDX License Identifier to be applied to
      a file was done in a spreadsheet of side by side results from of the
      output of two independent scanners (ScanCode & Windriver) producing SPDX
      tag:value files created by Philippe Ombredanne.  Philippe prepared the
      base worksheet, and did an initial spot review of a few 1000 files.
      
      The 4.13 kernel was the starting point of the analysis with 60,537 files
      assessed.  Kate Stewart did a file by file comparison of the scanner
      results in the spreadsheet to determine which SPDX license identifier(s)
      to be applied to the file. She confirmed any determination that was not
      immediately clear with lawyers working with the Linux Foundation.
      
      Criteria used to select files for SPDX license identifier tagging was:
       - Files considered eligible had to be source code files.
       - Make and config files were included as candidates if they contained >5
         lines of source
       - File already had some variant of a license header in it (even if <5
         lines).
      
      All documentation files were explicitly excluded.
      
      The following heuristics were used to determine which SPDX license
      identifiers to apply.
      
       - when both scanners couldn't find any license traces, file was
         considered to have no license information in it, and the top level
         COPYING file license applied.
      
         For non */uapi/* files that summary was:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|-------
         GPL-2.0                                              11139
      
         and resulted in the first patch in this series.
      
         If that file was a */uapi/* path one, it was "GPL-2.0 WITH
         Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|-------
         GPL-2.0 WITH Linux-syscall-note                        930
      
         and resulted in the second patch in this series.
      
       - if a file had some form of licensing information in it, and was one
         of the */uapi/* ones, it was denoted with the Linux-syscall-note if
         any GPL family license was found in the file or had no licensing in
         it (per prior point).  Results summary:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|------
         GPL-2.0 WITH Linux-syscall-note                       270
         GPL-2.0+ WITH Linux-syscall-note                      169
         ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
         ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
         LGPL-2.1+ WITH Linux-syscall-note                      15
         GPL-1.0+ WITH Linux-syscall-note                       14
         ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
         LGPL-2.0+ WITH Linux-syscall-note                       4
         LGPL-2.1 WITH Linux-syscall-note                        3
         ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
         ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1
      
         and that resulted in the third patch in this series.
      
       - when the two scanners agreed on the detected license(s), that became
         the concluded license(s).
      
       - when there was disagreement between the two scanners (one detected a
         license but the other didn't, or they both detected different
         licenses) a manual inspection of the file occurred.
      
       - In most cases a manual inspection of the information in the file
         resulted in a clear resolution of the license that should apply (and
         which scanner probably needed to revisit its heuristics).
      
       - When it was not immediately clear, the license identifier was
         confirmed with lawyers working with the Linux Foundation.
      
       - If there was any question as to the appropriate license identifier,
         the file was flagged for further research and to be revisited later
         in time.
      
      In total, over 70 hours of logged manual review was done on the
      spreadsheet to determine the SPDX license identifiers to apply to the
      source files by Kate, Philippe, Thomas and, in some cases, confirmation
      by lawyers working with the Linux Foundation.
      
      Kate also obtained a third independent scan of the 4.13 code base from
      FOSSology, and compared selected files where the other two scanners
      disagreed against that SPDX file, to see if there was new insights.  The
      Windriver scanner is based on an older version of FOSSology in part, so
      they are related.
      
      Thomas did random spot checks in about 500 files from the spreadsheets
      for the uapi headers and agreed with SPDX license identifier in the
      files he inspected. For the non-uapi files Thomas did random spot checks
      in about 15000 files.
      
      In initial set of patches against 4.14-rc6, 3 files were found to have
      copy/paste license identifier errors, and have been fixed to reflect the
      correct identifier.
      
      Additionally Philippe spent 10 hours this week doing a detailed manual
      inspection and review of the 12,461 patched files from the initial patch
      version early this week with:
       - a full scancode scan run, collecting the matched texts, detected
         license ids and scores
       - reviewing anything where there was a license detected (about 500+
         files) to ensure that the applied SPDX license was correct
       - reviewing anything where there was no detection but the patch license
         was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
         SPDX license was correct
      
      This produced a worksheet with 20 files needing minor correction.  This
      worksheet was then exported into 3 different .csv files for the
      different types of files to be modified.
      
      These .csv files were then reviewed by Greg.  Thomas wrote a script to
      parse the csv files and add the proper SPDX tag to the file, in the
      format that the file expected.  This script was further refined by Greg
      based on the output to detect more types of files automatically and to
      distinguish between header and source .c files (which need different
      comment types.)  Finally Greg ran the script using the .csv files to
      generate the patches.
      Reviewed-by: default avatarKate Stewart <kstewart@linuxfoundation.org>
      Reviewed-by: default avatarPhilippe Ombredanne <pombredanne@nexb.com>
      Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b2441318
  21. 01 Nov, 2017 2 commits
    • Ming Lei's avatar
      blk-mq-sched: improve dispatching from sw queue · b347689f
      Ming Lei authored
      SCSI devices use host-wide tagset, and the shared driver tag space is
      often quite big. However, there is also a queue depth for each lun(
      .cmd_per_lun), which is often small, for example, on both lpfc and
      qla2xxx, .cmd_per_lun is just 3.
      
      So lots of requests may stay in sw queue, and we always flush all
      belonging to same hw queue and dispatch them all to driver.
      Unfortunately it is easy to cause queue busy because of the small
      .cmd_per_lun.  Once these requests are flushed out, they have to stay in
      hctx->dispatch, and no bio merge can happen on these requests, and
      sequential IO performance is harmed.
      
      This patch introduces blk_mq_dequeue_from_ctx for dequeuing a request
      from a sw queue, so that we can dispatch them in scheduler's way. We can
      then avoid dequeueing too many requests from sw queue, since we don't
      flush ->dispatch completely.
      
      This patch improves dispatching from sw queue by using the .get_budget
      and .put_budget callbacks.
      Reviewed-by: default avatarOmar Sandoval <osandov@fb.com>
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      b347689f
    • Ming Lei's avatar
      blk-mq: introduce .get_budget and .put_budget in blk_mq_ops · de148297
      Ming Lei authored
      For SCSI devices, there is often a per-request-queue depth, which needs
      to be respected before queuing one request.
      
      Currently blk-mq always dequeues the request first, then calls
      .queue_rq() to dispatch the request to lld. One obvious issue with this
      approach is that I/O merging may not be successful, because when the
      per-request-queue depth can't be respected, .queue_rq() has to return
      BLK_STS_RESOURCE, and then this request has to stay in hctx->dispatch
      list. This means it never gets a chance to be merged with other IO.
      
      This patch introduces .get_budget and .put_budget callback in blk_mq_ops,
      then we can try to get reserved budget first before dequeuing request.
      If the budget for queueing I/O can't be satisfied, we don't need to
      dequeue request at all. Hence the request can be left in the IO
      scheduler queue, for more merging opportunities.
      Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      de148297
  22. 11 Sep, 2017 1 commit
    • Jens Axboe's avatar
      block: directly insert blk-mq request from blk_insert_cloned_request() · 157f377b
      Jens Axboe authored
      A NULL pointer crash was reported for the case of having the BFQ IO
      scheduler attached to the underlying blk-mq paths of a DM multipath
      device.  The crash occured in blk_mq_sched_insert_request()'s call to
      e->type->ops.mq.insert_requests().
      
      Paolo Valente correctly summarized why the crash occured with:
      "the call chain (dm_mq_queue_rq -> map_request -> setup_clone ->
      blk_rq_prep_clone) creates a cloned request without invoking
      e->type->ops.mq.prepare_request for the target elevator e.  The cloned
      request is therefore not initialized for the scheduler, but it is
      however inserted into the scheduler by blk_mq_sched_insert_request."
      
      All said, a request-based DM multipath device's IO scheduler should be
      the only one used -- when the original requests are issued to the
      underlying paths as cloned requests they are inserted directly in the
      underlying dispatch queue(s) rather than through an additional elevator.
      
      But commit bd166ef1 ("blk-mq-sched: add framework for MQ capable IO
      schedulers") switched blk_insert_cloned_request() from using
      blk_mq_insert_request() to blk_mq_sched_insert_request().  Which
      incorrectly added elevator machinery into a call chain that isn't
      supposed to have any.
      
      To fix this introduce a blk-mq private blk_mq_request_bypass_insert()
      that blk_insert_cloned_request() calls to insert the request without
      involving any elevator that may be attached to the cloned request's
      request_queue.
      
      Fixes: bd166ef1 ("blk-mq-sched: add framework for MQ capable IO schedulers")
      Cc: stable@vger.kernel.org
      Reported-by: default avatarBart Van Assche <Bart.VanAssche@wdc.com>
      Tested-by: default avatarMike Snitzer <snitzer@redhat.com>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      157f377b
  23. 09 Aug, 2017 1 commit
  24. 28 Jun, 2017 1 commit
  25. 18 Jun, 2017 2 commits