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scsi: core: avoid host-wide host_busy counter for scsi_mq

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It isn't necessary to check the host depth in scsi_queue_rq() any more
since it has been respected by blk-mq before calling scsi_queue_rq() via
getting driver tag.

Lots of LUNs may attach to same host and per-host IOPS may reach millions,
so we should avoid expensive atomic operations on the host-wide counter in
the IO path.

This patch implements scsi_host_busy() via blk_mq_tagset_busy_iter() with
one scsi command state for reading the count of busy IOs for scsi_mq.

It is observed that IOPS is increased by 15% in IO test on scsi_debug (32
LUNs, 32 submit queues, 1024 can_queue, libaio/dio) in a dual-socket
system.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ewan D. Milne <emilne@redhat.com>
Cc: Omar Sandoval <osandov@fb.com>,
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Cc: James Bottomley <james.bottomley@hansenpartnership.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20191025065855.6309-1-ming.lei@redhat.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Ming Lei
2019-10-25 14:58:55 +08:00
committed by Martin K. Petersen
parent 7f674c38a3
commit 6eb045e092
6 changed files with 44 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
include/scsi/scsi_cmnd.h
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@@ -63,6 +63,7 @@ struct scsi_pointer {
/* for scmd->state */
#define SCMD_STATE_COMPLETE 0
#define SCMD_STATE_INFLIGHT 1
struct scsi_cmnd {
struct scsi_request req;

3
include/scsi/scsi_host.h
View File

@@ -345,7 +345,7 @@ struct scsi_host_template {
/*
* This determines if we will use a non-interrupt driven
* or an interrupt driven scheme. It is set to the maximum number
* of simultaneous commands a given host adapter will accept.
* of simultaneous commands a single hw queue in HBA will accept.
*/
int can_queue;
@@ -554,7 +554,6 @@ struct Scsi_Host {
/* Area to keep a shared tag map */
struct blk_mq_tag_set tag_set;
atomic_t host_busy; /* commands actually active on low-level */
atomic_t host_blocked;
unsigned int host_failed; /* commands that failed.