scsi: core: avoid host-wide host_busy counter for scsi_mq
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() 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.
[mkp: clarified commit message]
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: Don Brace <don.brace@microsemi.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a1a0a29..600c780 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -345,7 +345,8 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost)
unsigned long flags;
rcu_read_lock();
- atomic_dec(&shost->host_busy);
+ if (!shost->use_blk_mq)
+ atomic_dec(&shost->host_busy);
if (unlikely(scsi_host_in_recovery(shost))) {
spin_lock_irqsave(shost->host_lock, flags);
if (shost->host_failed || shost->host_eh_scheduled)
@@ -444,7 +445,12 @@ static inline bool scsi_target_is_busy(struct scsi_target *starget)
static inline bool scsi_host_is_busy(struct Scsi_Host *shost)
{
- if (shost->can_queue > 0 &&
+ /*
+ * blk-mq can handle host queue busy efficiently via host-wide driver
+ * tag allocation
+ */
+
+ if (!shost->use_blk_mq && shost->can_queue > 0 &&
atomic_read(&shost->host_busy) >= shost->can_queue)
return true;
if (atomic_read(&shost->host_blocked) > 0)
@@ -1600,9 +1606,12 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
if (scsi_host_in_recovery(shost))
return 0;
- busy = atomic_inc_return(&shost->host_busy) - 1;
+ if (!shost->use_blk_mq)
+ busy = atomic_inc_return(&shost->host_busy) - 1;
+ else
+ busy = 0;
if (atomic_read(&shost->host_blocked) > 0) {
- if (busy)
+ if (busy || scsi_host_busy(shost))
goto starved;
/*
@@ -1616,7 +1625,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
"unblocking host at zero depth\n"));
}
- if (shost->can_queue > 0 && busy >= shost->can_queue)
+ if (!shost->use_blk_mq && shost->can_queue > 0 && busy >= shost->can_queue)
goto starved;
if (shost->host_self_blocked)
goto starved;
@@ -1702,7 +1711,9 @@ static void scsi_kill_request(struct request *req, struct request_queue *q)
* with the locks as normal issue path does.
*/
atomic_inc(&sdev->device_busy);
- atomic_inc(&shost->host_busy);
+
+ if (!shost->use_blk_mq)
+ atomic_inc(&shost->host_busy);
if (starget->can_queue > 0)
atomic_inc(&starget->target_busy);