Merge CAM locking changes from the projects/camlock branch to radically

reduce lock congestion and improve SMP scalability of the SCSI/ATA stack,
preparing the ground for the coming next GEOM direct dispatch support.

Replace big per-SIM locks with bunch of smaller ones:
 - per-LUN locks to protect device and peripheral drivers state;
 - per-target locks to protect list of LUNs on target;
 - per-bus locks to protect reference counting;
 - per-send queue locks to protect queue of CCBs to be sent;
 - per-done queue locks to protect queue of completed CCBs;
 - remaining per-SIM locks now protect only HBA driver internals.

While holding LUN lock it is allowed (while not recommended for performance
reasons) to take SIM lock.  The opposite acquisition order is forbidden.
All the other locks are leaf locks, that can be taken anywhere, but should
not be cascaded.  Many functions, such as: xpt_action(), xpt_done(),
xpt_async(), xpt_create_path(), etc. are no longer require (but allow) SIM
lock to be held.

To keep compatibility and solve cases where SIM lock can't be dropped, all
xpt_async() calls in addition to xpt_done() calls are queued to completion
threads for async processing in clean environment without SIM lock held.

Instead of single CAM SWI thread, used for commands completion processing
before, use multiple (depending on number of CPUs) threads.  Load balanced
between them using "hash" of the device B:T:L address.

HBA drivers that can drop SIM lock during completion processing and have
sufficient number of completion threads to efficiently scale to multiple
CPUs can use new function xpt_done_direct() to avoid extra context switch.
Make ahci(4) driver to use this mechanism depending on hardware setup.

Sponsored by:	iXsystems, Inc.
MFC after:	2 months

1 files changed, 7 insertions, 4 deletions

diff --git a/sys/cam/cam_queue.h b/sys/cam/cam_queue.h
index 0bb449117662..0f74e8241a40 100644
--- a/sys/cam/cam_queue.h
+++ b/sys/cam/cam_queue.h
@@ -33,6 +33,8 @@
 
 #ifdef _KERNEL
 
+#include <sys/lock.h>
+#include <sys/mutex.h>
 #include <sys/queue.h>
 #include <cam/cam.h>
 
@@ -59,8 +61,8 @@ struct cam_ccbq {
 	struct	camq queue;
 	struct ccb_hdr_tailq	queue_extra_head;
 	int	queue_extra_entries;
+	int	total_openings;
 	int	devq_openings;
-	int	devq_allocating;
 	int	dev_openings;
 	int	dev_active;
 	int	held;
@@ -69,9 +71,10 @@ struct cam_ccbq {
 struct cam_ed;
 
 struct cam_devq {
-	struct	camq send_queue;
-	int	send_openings;
-	int	send_active;
+	struct mtx	 send_mtx;
+	struct camq	 send_queue;
+	int		 send_openings;
+	int		 send_active;
 };