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authorMing Lei <[email protected]>2018-06-24 22:03:27 +0800
committerMartin K. Petersen <[email protected]>2018-06-26 12:53:26 -0400
commit328728630d9f2bf14b82ca30b5e47489beefe361 (patch)
treee9dd026ef5a248dc35190e8bb3f2c23063283be2
parentc84b023a4c1461498abf0eda54f60e2fd64a1ca2 (diff)
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 <[email protected]>, Cc: "Martin K. Petersen" <[email protected]>, Cc: James Bottomley <[email protected]>, Cc: Christoph Hellwig <[email protected]>, Cc: Don Brace <[email protected]> Cc: Kashyap Desai <[email protected]> Cc: Mike Snitzer <[email protected]> Cc: Hannes Reinecke <[email protected]> Cc: Laurence Oberman <[email protected]> Cc: Bart Van Assche <[email protected]> Signed-off-by: Ming Lei <[email protected]> Reviewed-by: Bart Van Assche <[email protected]> Signed-off-by: Martin K. Petersen <[email protected]>
-rw-r--r--drivers/scsi/hosts.c24
-rw-r--r--drivers/scsi/scsi_lib.c23
2 files changed, 40 insertions, 7 deletions
diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index ea4b0bb0c1cd..f02dcc875a09 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -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);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a1a0a2903263..600c78065d62 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);