scsi: iscsi: Register sysfs for iscsi workqueue

This patch enables setting cpu affinity through "cpumask" for iscsi
workqueues (iscsi_q_xx and iscsi_eh), so as to get performance isolation.

The max number of active worker was changed form 1 to 2, because "cpumask"
of ordered workqueue isn't allowed to change.

Link: https://lore.kernel.org/r/20200505011908.15538-1-bob.liu@oracle.com
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -2627,7 +2627,9 @@ struct Scsi_Host *iscsi_host_alloc(struct scsi_host_template *sht,
 	if (xmit_can_sleep) {
 		snprintf(ihost->workq_name, sizeof(ihost->workq_name),
 			"iscsi_q_%d", shost->host_no);
-		ihost->workq = create_singlethread_workqueue(ihost->workq_name);
+		ihost->workq = alloc_workqueue("%s",
+			WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_UNBOUND,
+			2, ihost->workq_name);
 		if (!ihost->workq)
 			goto free_host;
 	}

drivers/scsi/scsi_transport_iscsi.c

@@ -4728,7 +4728,9 @@ static __init int iscsi_transport_init(void)
 		goto unregister_flashnode_bus;
 	}
 
-	iscsi_eh_timer_workq = create_singlethread_workqueue("iscsi_eh");
+	iscsi_eh_timer_workq = alloc_workqueue("%s",
+			WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_UNBOUND,
+			2, "iscsi_eh");
 	if (!iscsi_eh_timer_workq) {
 		err = -ENOMEM;
 		goto release_nls;