[PATCH 2/4] scsi_dh: rdac handler: Make rdac hardware handler async

[Chandra Seetharaman <sekharan@us.ibm.com>]

Batch up MODE_SELECT in rdac device handler.

LSI RDAC storage has the capability of handling mode selects for
multiple luns in a same command. Make use of that ability to send
as few MODE SELECTs as possible to the storage controller as possible.

This patch creates a work queue and queues up activate requests
when a MODE SELECT is sent down the wire. When that MODE SELECT 
completes, it compiles queued up activate requests for multiple
luns into a single MODE SELECT.

This reduces the time to do failover/failback of large number of LUNS.

Signed-off-by: Babu Moger <babu.moger@lsi.com>
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>

---
 drivers/scsi/device_handler/scsi_dh_rdac.c |  117 ++++++++++++++++++++++++++---
 1 file changed, 104 insertions(+), 13 deletions(-)

Index: linux-2.6.31/drivers/scsi/device_handler/scsi_dh_rdac.c
===================================================================
--- linux-2.6.31.orig/drivers/scsi/device_handler/scsi_dh_rdac.c
+++ linux-2.6.31/drivers/scsi/device_handler/scsi_dh_rdac.c
@@ -22,6 +22,7 @@
 #include <scsi/scsi.h>
 #include <scsi/scsi_eh.h>
 #include <scsi/scsi_dh.h>
+#include <linux/workqueue.h>
 
 #define RDAC_NAME "rdac"
 #define RDAC_RETRY_COUNT 5
@@ -135,6 +136,11 @@ struct rdac_controller {
 		struct rdac_pg_legacy legacy;
 		struct rdac_pg_expanded expanded;
 	} mode_select;
+	spinlock_t		ms_lock;
+	int			ms_queued;
+	struct work_struct	ms_work;
+	struct scsi_device	*ms_sdev;
+	struct list_head	ms_head;
 };
 struct c8_inquiry {
 	u8	peripheral_info;
@@ -195,8 +201,17 @@ static const char *lun_state[] =
 	"owned (AVT mode)",
 };
 
+struct rdac_queue_data {
+	struct list_head	entry;
+	struct rdac_dh_data	*h;
+	activate_complete	callback_fn;
+	void			*callback_data;
+};
+
 static LIST_HEAD(ctlr_list);
 static DEFINE_SPINLOCK(list_lock);
+static struct workqueue_struct *kmpath_rdacd;
+static void send_mode_select(struct work_struct *work);
 
 static inline struct rdac_dh_data *get_rdac_data(struct scsi_device *sdev)
 {
@@ -253,7 +268,6 @@ static struct request *rdac_failover_get
 		rdac_pg->subpage_code = 0x1;
 		rdac_pg->page_len[0] = 0x01;
 		rdac_pg->page_len[1] = 0x28;
-		rdac_pg->lun_table[h->lun] = 0x81;
 	} else {
 		struct rdac_pg_legacy *rdac_pg;
 
@@ -263,7 +277,6 @@ static struct request *rdac_failover_get
 		common = &rdac_pg->common;
 		rdac_pg->page_code = RDAC_PAGE_CODE_REDUNDANT_CONTROLLER;
 		rdac_pg->page_len = 0x68;
-		rdac_pg->lun_table[h->lun] = 0x81;
 	}
 	common->rdac_mode[1] = RDAC_MODE_TRANSFER_SPECIFIED_LUNS;
 	common->quiescence_timeout = RDAC_QUIESCENCE_TIME;
@@ -297,6 +310,7 @@ static void release_controller(struct kr
 	struct rdac_controller *ctlr;
 	ctlr = container_of(kref, struct rdac_controller, kref);
 
+	flush_workqueue(kmpath_rdacd);
 	spin_lock(&list_lock);
 	list_del(&ctlr->node);
 	spin_unlock(&list_lock);
@@ -326,6 +340,11 @@ static struct rdac_controller *get_contr
 	memcpy(ctlr->slot_id, slot_id, SLOT_ID_LEN);
 	kref_init(&ctlr->kref);
 	ctlr->use_ms10 = -1;
+	ctlr->ms_queued = 0;
+	ctlr->ms_sdev = NULL;
+	spin_lock_init(&ctlr->ms_lock);
+	INIT_WORK(&ctlr->ms_work, send_mode_select);
+	INIT_LIST_HEAD(&ctlr->ms_head);
 	list_add(&ctlr->node, &ctlr_list);
 done:
 	spin_unlock(&list_lock);
@@ -445,8 +464,7 @@ static int set_mode_select(struct scsi_d
 	return err;
 }
 
-static int mode_select_handle_sense(struct scsi_device *sdev,
-				    unsigned char *sensebuf)
+static int mode_select_handle_sense(unsigned char *sensebuf)
 {
 	struct scsi_sense_hdr sense_hdr;
 	int err = SCSI_DH_IO, ret;
@@ -478,7 +496,7 @@ static int mode_select_handle_sense(stru
 			err = SCSI_DH_RETRY;
 		break;
 	default:
-		sdev_printk(KERN_INFO, sdev,
+		printk(KERN_INFO
 			    "MODE_SELECT failed with sense %02x/%02x/%02x.\n",
 			    sense_hdr.sense_key, sense_hdr.asc, sense_hdr.ascq);
 	}
@@ -487,11 +505,29 @@ done:
 	return err;
 }
 
-static int send_mode_select(struct scsi_device *sdev, struct rdac_dh_data *h)
+static void send_mode_select(struct work_struct *work)
 {
+	struct rdac_controller *ctlr =
+		container_of(work, struct rdac_controller, ms_work);
 	struct request *rq;
+	struct scsi_device *sdev = ctlr->ms_sdev;
+	struct rdac_dh_data *h = get_rdac_data(sdev);
 	struct request_queue *q = sdev->request_queue;
 	int err, retry_cnt = RDAC_RETRY_COUNT;
+	struct rdac_queue_data *tmp, *qdata;
+	LIST_HEAD(list);
+	u8 *lun_table;
+
+	spin_lock(&ctlr->ms_lock);
+	list_splice_init(&ctlr->ms_head, &list);
+	ctlr->ms_queued = 0;
+	ctlr->ms_sdev = NULL;
+	spin_unlock(&ctlr->ms_lock);
+
+	if (ctlr->use_ms10)
+		lun_table = ctlr->mode_select.expanded.lun_table;
+	else
+		lun_table = ctlr->mode_select.legacy.lun_table;
 
 retry:
 	err = SCSI_DH_RES_TEMP_UNAVAIL;
@@ -499,13 +535,17 @@ retry:
 	if (!rq)
 		goto done;
 
-	sdev_printk(KERN_INFO, sdev, "%s MODE_SELECT command.\n",
+ 	list_for_each_entry(qdata, &list, entry) {
+		lun_table[qdata->h->lun] = 0x81;
+	}
+
+	printk(KERN_INFO "%s MODE_SELECT command.\n",
 		(retry_cnt == RDAC_RETRY_COUNT) ? "queueing" : "retrying");
 
 	err = blk_execute_rq(q, NULL, rq, 1);
 	blk_put_request(rq);
 	if (err != SCSI_DH_OK) {
-		err = mode_select_handle_sense(sdev, h->sense);
+		err = mode_select_handle_sense(h->sense);
 		if (err == SCSI_DH_RETRY && retry_cnt--)
 			goto retry;
 	}
@@ -513,10 +553,45 @@ retry:
 		h->state = RDAC_STATE_ACTIVE;
 
 done:
-	return err;
+	list_for_each_entry_safe(qdata, tmp, &list, entry) {
+		list_del(&qdata->entry);
+		if (err == SCSI_DH_OK)
+			qdata->h->state = RDAC_STATE_ACTIVE;
+		if (qdata->callback_fn)
+			qdata->callback_fn(qdata->callback_data, err);
+		kfree(qdata);
+	}
+	return;
 }
 
-static int rdac_activate(struct scsi_device *sdev, activate_complete fn, void *data)
+static int queue_mode_select(struct scsi_device *sdev,
+				activate_complete fn, void *data)
+{
+	struct rdac_queue_data *qdata;
+	struct rdac_controller *ctlr;
+
+	qdata = kzalloc(sizeof(*qdata), GFP_KERNEL);
+	if (!qdata)
+		return SCSI_DH_RETRY;
+
+ 	qdata->h = get_rdac_data(sdev);
+	qdata->callback_fn = fn;
+	qdata->callback_data = data;
+
+	ctlr = qdata->h->ctlr;
+	spin_lock(&ctlr->ms_lock);
+	list_add_tail(&qdata->entry, &ctlr->ms_head);
+	if (!ctlr->ms_queued) {
+		ctlr->ms_queued = 1;
+		ctlr->ms_sdev = sdev;
+		queue_work(kmpath_rdacd, &ctlr->ms_work);
+	}
+	spin_unlock(&ctlr->ms_lock);
+	return SCSI_DH_OK;
+}
+
+static int rdac_activate(struct scsi_device *sdev,
+				activate_complete fn, void *data)
 {
 	struct rdac_dh_data *h = get_rdac_data(sdev);
 	int err = SCSI_DH_OK;
@@ -536,8 +611,11 @@ static int rdac_activate(struct scsi_dev
 		if (err != SCSI_DH_OK)
 			goto done;
 	}
-	if (h->lun_state == RDAC_LUN_UNOWNED)
-		err = send_mode_select(sdev, h);
+	if (h->lun_state == RDAC_LUN_UNOWNED) {
+		err = queue_mode_select(sdev, fn, data);
+		if (err == SCSI_DH_OK)
+			return 0;
+	}
 done:
 	if (fn)
 		fn(data, err);
@@ -726,13 +804,26 @@ static int __init rdac_init(void)
 	int r;
 
 	r = scsi_register_device_handler(&rdac_dh);
-	if (r != 0)
+	if (r != 0) {
 		printk(KERN_ERR "Failed to register scsi device handler.");
+		goto done;
+	}
+
+	/*
+	 * Create workqueue to handle mode selects for rdac
+	 */
+	kmpath_rdacd = create_singlethread_workqueue("kmpath_rdacd");
+	if (!kmpath_rdacd) {
+		scsi_unregister_device_handler(&rdac_dh);
+		printk(KERN_ERR "kmpath_rdacd creation failed.\n");
+	}
+done:
 	return r;
 }
 
 static void __exit rdac_exit(void)
 {
+	destroy_workqueue(kmpath_rdacd);
 	scsi_unregister_device_handler(&rdac_dh);
 }