Re: [PATCH V4 08/12] blk-mq: return budget token from .get_budget callback

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On 11/16/20 10:07 AM, Ming Lei wrote:
SCSI uses one global atomic variable to track queue depth for each
LUN/request queue.

This way doesn't scale well when there is lots of CPU cores and the
disk is very fast. It has been observed that IOPS is affected a lot
by tracking queue depth via sdev->device_busy in IO path.

Return budget token from .get_budget callback, and the budget token
can be passed to driver, so that we can replace the atomic variable
with sbitmap_queue, then the scale issue can be fixed.

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>
Tested-by: Sumanesh Samanta <sumanesh.samanta@xxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
  block/blk-mq-sched.c    | 17 +++++++++++++----
  block/blk-mq.c          | 36 +++++++++++++++++++++++++-----------
  block/blk-mq.h          | 25 +++++++++++++++++++++----
  drivers/scsi/scsi_lib.c | 16 +++++++++++-----
  include/linux/blk-mq.h  |  4 ++--
  5 files changed, 72 insertions(+), 26 deletions(-)
Reviewed-by: Hannes Reinecke <hare@xxxxxxx

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@xxxxxxx                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



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