scsi: convert host_busy to atomic_t
Avoid taking the host-wide host_lock to check the per-host queue limit.
Instead we do an atomic_inc_return early on to grab our slot in the queue,
and if necessary decrement it after finishing all checks.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index b2bc519..51f7911 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -582,13 +582,9 @@
*/
struct blk_queue_tag *bqt;
- /*
- * The following two fields are protected with host_lock;
- * however, eh routines can safely access during eh processing
- * without acquiring the lock.
- */
- unsigned int host_busy; /* commands actually active on low-level */
- unsigned int host_failed; /* commands that failed. */
+ atomic_t host_busy; /* commands actually active on low-level */
+ unsigned int host_failed; /* commands that failed.
+ protected by host_lock */
unsigned int host_eh_scheduled; /* EH scheduled without command */
unsigned int host_no; /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */