scsi: add use_cmd_list flag

Add a use_cmd_list flag in struct Scsi_Host to request keeping track of
all outstanding commands per device.

Default behaviour is not to keep track of cmd_list per sdev, as this may
introduce lock contention. (overhead is more on multi-node NUMA.), and
only enable it on the two drivers that need it.

Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/aacraid/linit.c

@@ -1152,6 +1152,7 @@ static int aac_probe_one(struct pci_dev *pdev, const struct pci_device_id *id)
 	shost->irq = pdev->irq;
 	shost->unique_id = unique_id;
 	shost->max_cmd_len = 16;
+	shost->use_cmd_list = 1;
 
 	aac = (struct aac_dev *)shost->hostdata;
 	aac->base_start = pci_resource_start(pdev, 0);

drivers/scsi/dpt_i2o.c

@@ -2363,6 +2363,7 @@ static s32 adpt_scsi_host_alloc(adpt_hba* pHba, struct scsi_host_template *sht)
 	host->unique_id = (u32)sys_tbl_pa + pHba->unit;
 	host->sg_tablesize = pHba->sg_tablesize;
 	host->can_queue = pHba->post_fifo_size;
+	host->use_cmd_list = 1;
 
 	return 0;
 }

drivers/scsi/scsi_lib.c

@@ -645,16 +645,18 @@ static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
 static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
 {
 	struct scsi_device *sdev = cmd->device;
+	struct Scsi_Host *shost = sdev->host;
 	unsigned long flags;
 
-	BUG_ON(list_empty(&cmd->list));
-
 	scsi_mq_free_sgtables(cmd);
 	scsi_uninit_cmd(cmd);
 
-	spin_lock_irqsave(&sdev->list_lock, flags);
-	list_del_init(&cmd->list);
-	spin_unlock_irqrestore(&sdev->list_lock, flags);
+	if (shost->use_cmd_list) {
+		BUG_ON(list_empty(&cmd->list));
+		spin_lock_irqsave(&sdev->list_lock, flags);
+		list_del_init(&cmd->list);
+		spin_unlock_irqrestore(&sdev->list_lock, flags);
+	}
 }
 
 /*
@@ -1815,13 +1817,11 @@ static int scsi_mq_prep_fn(struct request *req)
 	INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
 	cmd->jiffies_at_alloc = jiffies;
 
-	/*
-	 * XXX: cmd_list lookups are only used by two drivers, try to get
-	 * rid of this list in common code.
-	 */
-	spin_lock_irq(&sdev->list_lock);
-	list_add_tail(&cmd->list, &sdev->cmd_list);
-	spin_unlock_irq(&sdev->list_lock);
+	if (shost->use_cmd_list) {
+		spin_lock_irq(&sdev->list_lock);
+		list_add_tail(&cmd->list, &sdev->cmd_list);
+		spin_unlock_irq(&sdev->list_lock);
+	}
 
 	sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt->cmd_size;
 	cmd->sdb.table.sgl = sg;

include/scsi/scsi_host.h

@@ -680,6 +680,7 @@ struct Scsi_Host {
 	unsigned no_write_same:1;
 
 	unsigned use_blk_mq:1;
+	unsigned use_cmd_list:1;
 
 	/*
 	 * Optional work queue to be utilized by the transport