[PATCH v5 0/3] Disable fair tag sharing for UFS devices

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

Hi Jens,

The fair tag sharing algorithm reduces performance for UFS devices
significantly. This is because UFS devices have multiple logical units, a
limited queue depth (32 for UFS 3.1 devices), because it happens often that
multiple logical units are accessed and also because it takes time to
give tags back after activity on a request queue has stopped. This patch series
restores UFS device performance to that of the legacy block layer by disabling
fair tag sharing for UFS devices.

Please consider this patch series for the next merge window.

Thanks,

Bart.

Changes compared to v4:
 - Rebased on top of kernel v6.7-rc1.

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(-)