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

This reverts commit 328728630d9f2bf14b82ca30b5e47489beefe361.

There is fundamental issue in commit 328728630d9f2bf1 (scsi: core: avoid
host-wide host_busy counter for scsi_mq) because SCSI's host busy counter
may not be same with counter of blk-mq's inflight tags, especially in case
of none io scheduler.

We may switch to other approach for addressing this scsi_mq's performance
issue, such as percpu counter or kind of ways, so revert this commit first
for fixing this kind of issue in EH path, as reported by Jens.

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>
Cc: Jens Axboe <axboe@kernel.dk>
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index f02dcc875a09a6c6ece63e89e8256c512e11f01e..ea4b0bb0c1cd4e6b12748256741afae339311591 100644 (file)
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -563,35 +563,13 @@ 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)
 {
-       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;
+       return atomic_read(&shost->host_busy);
 }
 EXPORT_SYMBOL(scsi_host_busy);
 

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1046679f5473c0ea8f2152c3c0603de217f768a1..eb97d2dd36516d0a3a5c0a9db1f255aaf5a9c56f 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -345,8 +345,7 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost)
        unsigned long flags;
 
        rcu_read_lock();
-       if (!shost->use_blk_mq)
-               atomic_dec(&shost->host_busy);
+       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)
@@ -445,12 +444,7 @@ static inline bool scsi_target_is_busy(struct scsi_target *starget)
 
 static inline bool scsi_host_is_busy(struct Scsi_Host *shost)
 {
-       /*
-        * blk-mq can handle host queue busy efficiently via host-wide driver
-        * tag allocation
-        */
-
-       if (!shost->use_blk_mq && shost->can_queue > 0 &&
+       if (shost->can_queue > 0 &&
            atomic_read(&shost->host_busy) >= shost->can_queue)
                return true;
        if (atomic_read(&shost->host_blocked) > 0)
@@ -1606,12 +1600,9 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
        if (scsi_host_in_recovery(shost))
                return 0;
 
-       if (!shost->use_blk_mq)
-               busy = atomic_inc_return(&shost->host_busy) - 1;
-       else
-               busy = 0;
+       busy = atomic_inc_return(&shost->host_busy) - 1;
        if (atomic_read(&shost->host_blocked) > 0) {
-               if (busy || scsi_host_busy(shost))
+               if (busy)
                        goto starved;
 
                /*
@@ -1625,7 +1616,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
                                     "unblocking host at zero depth\n"));
        }
 
-       if (!shost->use_blk_mq && shost->can_queue > 0 && busy >= shost->can_queue)
+       if (shost->can_queue > 0 && busy >= shost->can_queue)
                goto starved;
        if (shost->host_self_blocked)
                goto starved;
@@ -1711,9 +1702,7 @@ 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);
-
-       if (!shost->use_blk_mq)
-               atomic_inc(&shost->host_busy);
+       atomic_inc(&shost->host_busy);
        if (starget->can_queue > 0)
                atomic_inc(&starget->target_busy);