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 four patches changes SCSI for switching to track device queue depth via sbitmap. The patchset have been tested by Broadcom, and obvious performance boost can be observed on megaraid_sas. V5: - add comment on sbitmap_weight() - add patch 'megaraid_sas: v2 replace sdev_busy with local counter' for fixing build failure V4: - limit max sdev->queue_depth as max(1024, shost->can_queue) - simplify code for moving per-cpu allocation hint into sbitmap V3: - rebase on both for-5.10/block and 5.10/scsi-queue. V2: - fix one build failure Kashyap Desai (1): megaraid_sas: v2 replace sdev_busy with local counter Ming Lei (12): sbitmap: remove sbitmap_clear_bit_unlock sbitmap: maintain allocation round_robin in sbitmap sbitmap: add helpers for updating allocation hint sbitmap: move allocation hint into sbitmap sbitmap: export sbitmap_weight sbitmap: add helper of sbitmap_calculate_shift blk-mq: add callbacks for storing & retrieving budget token blk-mq: return budget token from .get_budget callback scsi: put hot fields of scsi_host_template into one cacheline scsi: add scsi_device_busy() to read sdev->device_busy scsi: make sure sdev->queue_depth is <= max(shost->can_queue, 1024) scsi: replace sdev->device_busy with sbitmap block/blk-mq-sched.c | 17 +- block/blk-mq.c | 38 ++-- block/blk-mq.h | 25 ++- block/kyber-iosched.c | 3 +- drivers/message/fusion/mptsas.c | 2 +- drivers/scsi/megaraid/megaraid_sas.h | 2 + drivers/scsi/megaraid/megaraid_sas_fusion.c | 47 ++++- drivers/scsi/mpt3sas/mpt3sas_scsih.c | 2 +- drivers/scsi/scsi.c | 13 ++ drivers/scsi/scsi_lib.c | 69 ++++--- drivers/scsi/scsi_priv.h | 3 + drivers/scsi/scsi_scan.c | 23 ++- drivers/scsi/scsi_sysfs.c | 4 +- drivers/scsi/sg.c | 2 +- include/linux/blk-mq.h | 13 +- include/linux/sbitmap.h | 85 +++++--- include/scsi/scsi_cmnd.h | 2 + include/scsi/scsi_device.h | 8 +- include/scsi/scsi_host.h | 72 ++++--- lib/sbitmap.c | 210 +++++++++++--------- 20 files changed, 427 insertions(+), 213 deletions(-) Cc: Omar Sandoval <osandov@xxxxxx> Cc: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx> Cc: Sumanesh Samanta <sumanesh.samanta@xxxxxxxxxxxx> Cc: Ewan D. Milne <emilne@xxxxxxxxxx> Cc: Hannes Reinecke <hare@xxxxxxx> -- 2.25.4
