[PATCH V4 0/8] block, bfq: extend bfq to support multi-actuator drives

[Paolo Valente]

Hi,

this V4 differs from V3 in that it implements all recommendations
provided by Damien Le Moal in the thread for V3 [2]. It also addresses
all the issues reported by the kernel test robot in the same thread.

Here is the whole description of this patch series again.  This
extension addresses the following issue. Single-LUN multi-actuator
SCSI drives, as well as all multi-actuator SATA 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/
[2] https://lore.kernel.org/lkml/20221004094010.80090-1-paolo.valente@xxxxxxxxxx/

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: move io_cq-persistent bfqq data into a dedicated struct
  block, bfq: turn bfqq_data into an array in bfq_io_cq

 block/bfq-cgroup.c  |  97 +++++----
 block/bfq-iosched.c | 518 ++++++++++++++++++++++++++++++--------------
 block/bfq-iosched.h | 141 +++++++++---
 block/bfq-wf2q.c    |   2 +-
 4 files changed, 523 insertions(+), 235 deletions(-)

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2.20.1