[PATCH v4 0/3] Support disabling fair tag sharing

[Bart Van Assche <bvanassche@acm.org>]

Hi Jens,

Performance of UFS devices is reduced significantly by the fair tag sharing
algorithm. This is because UFS devices have multiple logical units and a
limited queue depth (32 for UFS 3.1 devices) and also because it takes time to
give tags back after activity on a request queue has stopped. This patch series
addresses this issue by introducing a flag that allows block drivers to
disable fair sharing.

Please consider this patch series for the next merge window.

Thanks,

Bart.

Changes compared to v3:
 - Instead of disabling fair tag sharing for all block drivers, introduce a flag
   for disabling it conditionally.

Changes between v2 and v3:
 - Rebased on top of the latest kernel.

Changes between v1 and v2:
 - Restored the tags->active_queues variable and thereby fixed the
   "uninitialized variable" warning reported by the kernel test robot.

Bart Van Assche (3):
  block: Introduce flag BLK_MQ_F_DISABLE_FAIR_TAG_SHARING
  scsi: core: Support disabling fair tag sharing
  scsi: ufs: Disable fair tag sharing

 block/blk-mq-debugfs.c    | 1 +
 block/blk-mq.h            | 3 ++-
 drivers/scsi/hosts.c      | 1 +
 drivers/scsi/scsi_lib.c   | 2 ++
 drivers/ufs/core/ufshcd.c | 1 +
 include/linux/blk-mq.h    | 1 +
 include/scsi/scsi_host.h  | 6 ++++++
 7 files changed, 14 insertions(+), 1 deletion(-)