[PATCH RFC 0/5] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs

[John Garry]

This is a 2nd stab at solving the problem of hostwide shared tags for SCSI
HBAs.

As discussed previously, Ming Lei's most recent series in [0] to use
hctx[0] tags for all hctx for a host was a bit messy and intrusive, so seen
as a no go. Indeed, blk-mq is designed for separate tags per hctx.

This series introduces a different approach to solve that problem, in
keeping the per-hctx tags but introducing a new separate shared set of
tags, which SCSI HBAs can use for a hostwide tags.

Adding support for shared tags should not have a significant performance
impact for when shared tags are not requested.

Currently I just fixed up the hisi_sas driver to use the shared tags,
but should not be much trouble to change others over.

Patch #3 is quite experimental at this point. I also threw in a minor
tidy-up patch.

[0] https://lore.kernel.org/linux-block/20190531022801.10003-1-ming.lei@xxxxxxxxxx/

Hannes Reinecke (1):
  scsi: Add template flag 'host_tagset'

John Garry (3):
  blk-mq: Remove some unused function arguments
  blk-mq: Facilitate a shared tags per tagset
  scsi: hisi_sas: Switch v3 hw to MQ

Ming Lei (1):
  blk-mq: rename BLK_MQ_F_TAG_SHARED as BLK_MQ_F_TAG_QUEUE_SHARED

 block/blk-core.c                       |  1 +
 block/blk-flush.c                      |  2 +
 block/blk-mq-debugfs.c                 |  4 +-
 block/blk-mq-tag.c                     | 91 +++++++++++++++++++++++++-
 block/blk-mq-tag.h                     |  8 +--
 block/blk-mq.c                         | 91 +++++++++++++++++++-------
 block/blk-mq.h                         | 11 +++-
 drivers/scsi/hisi_sas/hisi_sas.h       |  3 +-
 drivers/scsi/hisi_sas/hisi_sas_main.c  | 43 ++++++------
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c | 85 ++++++++++--------------
 drivers/scsi/scsi_lib.c                |  2 +
 include/linux/blk-mq.h                 |  5 +-
 include/linux/blkdev.h                 |  1 +
 include/scsi/scsi_host.h               |  3 +
 14 files changed, 242 insertions(+), 108 deletions(-)

-- 
2.17.1