[PATCH 0/4] scis: don't apply per-LUN queue depth for SSD

[Ming Lei <ming.lei@redhat.com>]

Hi,

SCSI's per-LUN queue depth is usually for improving IO merge and
balancing IO load among LUNs. blk-mq has provides fair driver tag
allocation and managed IRQ balances interrupt load among queues,
meantime IO merge doesn't play a big role for SSD, and NVMe doesn't
apply per-namespace queue depth.

This patchset tries to don't apply per-LUN queue depth for SSD, then
we can avoid the expensive atomic operation on sdev->device_busy.
We do understand that this shared counter affects IOPS a lot.

The 1st two patches replaces .device_busy with two private counter for
megaraid_sas and mpt3sas to track inflight per-LUN commands since the
two drivers need the counter for balancing load, even though it is
probably no much use.

The last two patches avoid to operate on sdev->device_busy in IO path
for SSD.


Ming Lei (4):
  scsi: megaraid_sas: use private counter for tracking inflight per-LUN
    commands
  scsi: mpt3sas: use private counter for tracking inflight per-LUN
    commands
  scsi: sd: register request queue after sd_revalidate_disk is done
  scsi: core: don't limit per-LUN queue depth for SSD

 block/blk-sysfs.c                           | 14 +++++++++++-
 drivers/scsi/megaraid/megaraid_sas.h        |  1 +
 drivers/scsi/megaraid/megaraid_sas_base.c   | 15 +++++++++++--
 drivers/scsi/megaraid/megaraid_sas_fusion.c | 13 +++++++----
 drivers/scsi/mpt3sas/mpt3sas_base.c         |  3 ++-
 drivers/scsi/mpt3sas/mpt3sas_base.h         |  1 +
 drivers/scsi/mpt3sas/mpt3sas_scsih.c        | 15 +++++++++++--
 drivers/scsi/scsi_lib.c                     | 24 +++++++++++++++------
 drivers/scsi/sd.c                           |  8 ++++++-
 9 files changed, 77 insertions(+), 17 deletions(-)

Cc: Sathya Prakash <sathya.prakash@broadcom.com>
Cc: Chaitra P B <chaitra.basappa@broadcom.com>
Cc: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
Cc: Hannes Reinecke <hare@suse.de>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
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2.20.1