[PATCH 00/10] scsi: tracking device queue depth via sbitmap

Ming Lei
2020-02-11T12:12:01Z

Hi,

scsi uses one global atomic variable to track queue depth for each
LUN/request queue. This way can't scale well when there is lots of CPU
cores and the disk is very fast. Broadcom guys has complained that their
high end HBA can't reach top performance because .device_busy is
operated in IO path.

Replace the atomic variable sdev->device_busy with sbitmap for
tracking scsi device queue depth.

Test on scsi_debug shows this way improve IOPS > 20%. Meantime
the IOPS difference is just ~1% compared with bypassing .device_busy
on scsi_debug via patches[1]

The 1st 6 patches moves percpu allocation hint into sbitmap, since
the improvement by doing percpu allocation hint on sbitmap is observable.
Meantime export helpers for SCSI.

Patch 7 and 8 prepares for the conversion by returning budget token
from .get_budget callback, meantime passes the budget token to driver
via 'struct blk_mq_queue_data' in .queue_rq().

The last two patches changes SCSI for switching to track device queue
depth via sbitmap.

Broadcom Guys, please test this patchset and see if expected performance
can be reached.

Please comment and review!

thanks,
Ming

[1] https://lore.kernel.org/linux-block/20200119071432.18558-6-ming.lei@redhat.com/

Ming Lei (10):
sbitmap: maintain allocation round_robin in sbitmap
sbitmap: add helpers for updating allocation hint
sbitmap: remove sbitmap_clear_bit_unlock
sbitmap: move allocation hint into sbitmap
sbitmap: export sbitmap_weight
sbitmap: add helper of sbitmap_calculate_shift
blk-mq: return budget token from .get_budget callback
blk-mq: pass budget token to dirver via blk_mq_queue_data
scsi: add scsi_device_busy() to read sdev->device_busy
scsi: replace sdev->device_busy with sbitmap

block/blk-mq-sched.c | 20 ++-
block/blk-mq.c | 37 +++--
block/blk-mq.h | 11 +-
block/kyber-iosched.c | 3 +-
drivers/dma/idxd/device.c | 2 +-
drivers/dma/idxd/submit.c | 2 +-
drivers/scsi/mpt3sas/mpt3sas_scsih.c | 2 +-
drivers/scsi/scsi.c | 2 +
drivers/scsi/scsi_lib.c | 47 +++---
drivers/scsi/scsi_priv.h | 1 +
drivers/scsi/scsi_scan.c | 21 ++-
drivers/scsi/scsi_sysfs.c | 4 +-
drivers/scsi/sg.c | 2 +-
include/linux/blk-mq.h | 5 +-
include/linux/sbitmap.h | 84 +++++++----
include/scsi/scsi_cmnd.h | 2 +
include/scsi/scsi_device.h | 8 +-
lib/sbitmap.c | 213 +++++++++++++++------------
18 files changed, 285 insertions(+), 181 deletions(-)