From 066e560b31f66d5eb628be945bff3460ed65b03a Mon Sep 17 00:00:00 2001
From: Peter Avalos <pavalos@dragonflybsd.org>
Date: Sun, 2 Dec 2007 05:30:08 +0000
Subject: [PATCH] Add a tunable that allows one to turn off the automatic
 sending of the ORDERED tag. This recoups significant performance gains for
 many arrays.

The default is still to send out the ORDERED tag periodically.

Obtained-from: FreeBSD
---
 sys/bus/cam/scsi/scsi_da.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/sys/bus/cam/scsi/scsi_da.c b/sys/bus/cam/scsi/scsi_da.c
index 85929c187f..b85fd428cb 100644
--- a/sys/bus/cam/scsi/scsi_da.c
+++ b/sys/bus/cam/scsi/scsi_da.c
@@ -26,7 +26,7 @@
  * SUCH DAMAGE.
  *
  * $FreeBSD: src/sys/cam/scsi/scsi_da.c,v 1.42.2.46 2003/10/21 22:18:19 thomas Exp $
- * $DragonFly: src/sys/bus/cam/scsi/scsi_da.c,v 1.50 2007/12/02 03:25:07 pavalos Exp $
+ * $DragonFly: src/sys/bus/cam/scsi/scsi_da.c,v 1.51 2007/12/02 05:30:08 pavalos Exp $
  */
 
 #ifdef _KERNEL
@@ -461,8 +461,13 @@ static void		dashutdown(void *arg, int howto);
 #define	DA_DEFAULT_RETRY	4
 #endif
 
+#ifndef	DA_DEFAULT_SEND_ORDERED
+#define	DA_DEFAULT_SEND_ORDERED	1
+#endif
+
 static int da_retry_count = DA_DEFAULT_RETRY;
 static int da_default_timeout = DA_DEFAULT_TIMEOUT;
+static int da_send_ordered = DA_DEFAULT_SEND_ORDERED;
 static struct callout dasendorderedtag_ch;
 
 SYSCTL_NODE(_kern_cam, OID_AUTO, da, CTLFLAG_RD, 0,
@@ -473,6 +478,9 @@ TUNABLE_INT("kern.cam.da.retry_count", &da_retry_count);
 SYSCTL_INT(_kern_cam_da, OID_AUTO, default_timeout, CTLFLAG_RW,
            &da_default_timeout, 0, "Normal I/O timeout (in seconds)");
 TUNABLE_INT("kern.cam.da.default_timeout", &da_default_timeout);
+SYSCTL_INT(_kern_cam_da, OID_AUTO, da_send_ordered, CTLFLAG_RW,
+           &da_send_ordered, 0, "Send Ordered Tags");
+TUNABLE_INT("kern.cam.da.da_send_ordered", &da_send_ordered);
 
 /*
  * DA_ORDEREDTAG_INTERVAL determines how often, relative
@@ -980,7 +988,7 @@ dainit(void)
 	if (status != CAM_REQ_CMP) {
 		kprintf("da: Failed to attach master async callback "
 		       "due to status 0x%x!\n", status);
-	} else {
+	} else if (da_send_ordered) {
 
 		/*
 		 * Schedule a periodic event to occasionally send an
@@ -2044,24 +2052,23 @@ dasendorderedtag(void *arg)
 {
 	struct da_softc *softc;
 
-	for (softc = SLIST_FIRST(&softc_list);
-	     softc != NULL;
-	     softc = SLIST_NEXT(softc, links)) {
-		crit_enter();
-		if ((softc->ordered_tag_count == 0) 
-		 && ((softc->flags & DA_FLAG_WENT_IDLE) == 0)) {
-			softc->flags |= DA_FLAG_NEED_OTAG;
+	if (da_send_ordered) {
+		SLIST_FOREACH(softc, &softc_list, links) {
+			crit_enter();
+			if ((softc->ordered_tag_count == 0) 
+			 && ((softc->flags & DA_FLAG_WENT_IDLE) == 0)) {
+				softc->flags |= DA_FLAG_NEED_OTAG;
+			}
+			if (softc->outstanding_cmds > 0)
+				softc->flags &= ~DA_FLAG_WENT_IDLE;
+			softc->ordered_tag_count = 0;
+			crit_exit();
 		}
-		if (softc->outstanding_cmds > 0)
-			softc->flags &= ~DA_FLAG_WENT_IDLE;
-
-		softc->ordered_tag_count = 0;
-		crit_exit();
+		/* Queue us up again */
+		callout_reset(&dasendorderedtag_ch,
+		    (da_default_timeout * hz) / DA_ORDEREDTAG_INTERVAL,
+		    dasendorderedtag, NULL);
 	}
-	/* Queue us up again */
-	callout_reset(&dasendorderedtag_ch,
-	    (da_default_timeout * hz) / DA_ORDEREDTAG_INTERVAL,
-	    dasendorderedtag, NULL);
 }
 
 /*
-- 
2.11.4.GIT