[PATCH V3 0/8] block, bfq: extend bfq to support multi-actuator drives

[Paolo Valente]

[I made a mistake, and the series did not compile, this V3 seems ok;
repeating below the same cover letter as V2]

Hi,
this is a new version of a patch series that extends BFQ so as to
optimize I/O dispatch to multi-actuator drives. The only difference
from the previous version is a fix in the invocation of bio_end_sector
in patch "block, bfq: retrieve independent access ranges from request
queue" (I have appended a -1 after such invocation). See [2] for
details on this fix.

Here is the general description of this patch series again.  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

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 | 490 +++++++++++++++++++++++++++++---------------
 block/bfq-iosched.h | 149 ++++++++++----
 block/bfq-wf2q.c    |   2 +-
 4 files changed, 495 insertions(+), 243 deletions(-)

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2.20.1