[PATCH 0/8] block, bfq: extend bfq to support multi-actuator drives

[Paolo Valente]

Hi,
this patch series extends BFQ so as to optimize I/O dispatch to
multi-actuator drives. In particular, this extension addresses the
following issue. Multi-actuator drives appear as a single device to
the I/O subsystem [1].  Yet they address commands to different
actuators internally, as a function of Logical Block Addressing
(LBAs). A given sector is reachable by only one of the actuators. For
example, Seagate’s Serial Advanced Technology Attachment (SATA)
version contains two actuators and maps the lower half of the SATA LBA
space to the lower actuator and the upper half to the upper actuator.

Evidently, to fully utilize actuators, no actuator must be left idle
or underutilized while there is pending I/O for it. To reach this
goal, the block layer must somehow control the load of each actuator
individually. This series enriches BFQ with such a per-actuator
control, as a first step. Then it also adds a simple mechanism for
guaranteeing that actuators with pending I/O are never left idle.

See [1] for a more detailed overview of the problem and of the
solutions implemented in this patch series. There you will also find
some preliminary performance results.

Thanks,
Paolo

[1] https://www.linaro.org/blog/budget-fair-queueing-bfq-linux-io-scheduler-optimizations-for-multi-actuator-sata-hard-drives/

Davide Zini (3):
  block, bfq: split also async bfq_queues on a per-actuator basis
  block, bfq: inject I/O to underutilized actuators
  block, bfq: balance I/O injection among underutilized actuators

Federico Gavioli (1):
  block, bfq: retrieve independent access ranges from request queue

Paolo Valente (4):
  block, bfq: split sync bfq_queues on a per-actuator basis
  block, bfq: forbid stable merging of queues associated with different
    actuators
  block, bfq: turn scalar fields into arrays in bfq_io_cq
  block, bfq: turn BFQ_NUM_ACTUATORS into BFQ_MAX_ACTUATORS

 block/bfq-cgroup.c  |  97 +++++----
 block/bfq-iosched.c | 488 +++++++++++++++++++++++++++++---------------
 block/bfq-iosched.h | 149 ++++++++++----
 block/bfq-wf2q.c    |   2 +-
 4 files changed, 493 insertions(+), 243 deletions(-)

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2.20.1