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[dm-devel] RE: [PATCH 2/4] scsi_dh: rdac handler: Make rdac hardware handler async



Hi Chandra,
I have tested these patches on 2.6.31 kernel with LSI storage.
My configuration had 234 Luns with two paths to each lun(one active, one  passive) and luns were evenly distributed. 
Here are the results.

Results with the patches
Failover takes about 1 minute to complete 117 mode selects. Failovers are completed in two sets(1 mode select first and then 116 mode selects together).
Failback takes about 2 and Half minutes.. 


Results without the patches on same configuration
failover takes about 12 minutes to complete 117 mode selects. 
Failback takes about 15 minutes.

Thanks
Babu Moger 

> -----Original Message-----
> From: linux-scsi-owner vger kernel org [mailto:linux-scsi-
> owner vger kernel org] On Behalf Of Chandra Seetharaman
> Sent: Tuesday, September 29, 2009 9:08 PM
> To: linux-scsi vger kernel org
> Cc: dm-devel redhat com; Moger, Babu; michaelc cs wisc edu;
> Benoit_Arthur emc com; Eddie Williams steeleye com;
> berthiaume_wayne emc com; Chandra Seetharaman
> Subject: [PATCH 2/4] scsi_dh: rdac handler: Make rdac hardware handler
> async
> 
> 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);
>  }
> 
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