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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>
This commit is contained in:
Ming Lei 2018-06-24 22:03:27 +08:00 committed by Martin K. Petersen
parent c84b023a4c
commit 328728630d
2 changed files with 40 additions and 7 deletions
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24
drivers/scsi/hosts.c
View File

@ -563,13 +563,35 @@ struct Scsi_Host *scsi_host_get(struct Scsi_Host *shost)
}
EXPORT_SYMBOL(scsi_host_get);
struct scsi_host_mq_in_flight {
int cnt;
};
static void scsi_host_check_in_flight(struct request *rq, void *data,
bool reserved)
{
struct scsi_host_mq_in_flight *in_flight = data;
if (blk_mq_request_started(rq))
in_flight->cnt++;
}
/**
* scsi_host_busy - Return the host busy counter
* @shost: Pointer to Scsi_Host to inc.
**/
int scsi_host_busy(struct Scsi_Host *shost)
{
return atomic_read(&shost->host_busy);
struct scsi_host_mq_in_flight in_flight = {
.cnt = 0,
};
if (!shost->use_blk_mq)
return atomic_read(&shost->host_busy);
blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight,
&in_flight);
return in_flight.cnt;
}
EXPORT_SYMBOL(scsi_host_busy);

23
drivers/scsi/scsi_lib.c
View File

@ -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);