target: use a workqueue for I/O completions

Instead of abusing the target processing thread for offloading I/O
completion in the backends to user context add a new workqueue.  This means
completions can be processed as fast as available CPU time allows it,
including in parallel with other completions and more importantly I/O
submission or QUEUE FULL retries.  This should give much better performance
especially on loaded systems.

As a fallout we can merge all the completed states into a single
one.

On the downside this change complicates lun reset handling a bit by
requiring us to cancel a work item only for those states that have it
initialized.  The alternative would be to either always initialize the work
item to a dummy handler, or always use the same handler and do a switch on
the state. The long term solution will be a flag that says that the command
has an initialized work item, but that's only going to be useful once we
have more users.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_tmr.c

@@ -255,6 +255,16 @@ static void core_tmr_drain_task_list(
 			atomic_read(&cmd->t_transport_stop),
 			atomic_read(&cmd->t_transport_sent));
 
+		/*
+		 * If the command may be queued onto a workqueue cancel it now.
+		 *
+		 * This is equivalent to removal from the execute queue in the
+		 * loop above, but we do it down here given that
+		 * cancel_work_sync may block.
+		 */
+		if (cmd->t_state == TRANSPORT_COMPLETE)
+			cancel_work_sync(&cmd->work);
+
 		spin_lock_irqsave(&cmd->t_state_lock, flags);
 		target_stop_task(task, &flags);
 

drivers/target/target_core_transport.c

@@ -58,6 +58,7 @@
 
 static int sub_api_initialized;
 
+static struct workqueue_struct *target_completion_wq;
 static struct kmem_cache *se_cmd_cache;
 static struct kmem_cache *se_sess_cache;
 struct kmem_cache *se_tmr_req_cache;
@@ -84,6 +85,8 @@ static int transport_generic_get_mem(struct se_cmd *cmd);
 static void transport_put_cmd(struct se_cmd *cmd);
 static void transport_remove_cmd_from_queue(struct se_cmd *cmd);
 static int transport_set_sense_codes(struct se_cmd *cmd, u8 asc, u8 ascq);
+static void transport_generic_request_failure(struct se_cmd *, int, int);
+static void target_complete_ok_work(struct work_struct *work);
 
 int init_se_kmem_caches(void)
 {
@@ -99,7 +102,7 @@ int init_se_kmem_caches(void)
 	if (!se_tmr_req_cache) {
 		pr_err("kmem_cache_create() for struct se_tmr_req"
 				" failed\n");
-		goto out;
+		goto out_free_cmd_cache;
 	}
 	se_sess_cache = kmem_cache_create("se_sess_cache",
 			sizeof(struct se_session), __alignof__(struct se_session),
@@ -107,14 +110,14 @@ int init_se_kmem_caches(void)
 	if (!se_sess_cache) {
 		pr_err("kmem_cache_create() for struct se_session"
 				" failed\n");
-		goto out;
+		goto out_free_tmr_req_cache;
 	}
 	se_ua_cache = kmem_cache_create("se_ua_cache",
 			sizeof(struct se_ua), __alignof__(struct se_ua),
 			0, NULL);
 	if (!se_ua_cache) {
 		pr_err("kmem_cache_create() for struct se_ua failed\n");
-		goto out;
+		goto out_free_sess_cache;
 	}
 	t10_pr_reg_cache = kmem_cache_create("t10_pr_reg_cache",
 			sizeof(struct t10_pr_registration),
@@ -122,7 +125,7 @@ int init_se_kmem_caches(void)
 	if (!t10_pr_reg_cache) {
 		pr_err("kmem_cache_create() for struct t10_pr_registration"
 				" failed\n");
-		goto out;
+		goto out_free_ua_cache;
 	}
 	t10_alua_lu_gp_cache = kmem_cache_create("t10_alua_lu_gp_cache",
 			sizeof(struct t10_alua_lu_gp), __alignof__(struct t10_alua_lu_gp),
@@ -130,7 +133,7 @@ int init_se_kmem_caches(void)
 	if (!t10_alua_lu_gp_cache) {
 		pr_err("kmem_cache_create() for t10_alua_lu_gp_cache"
 				" failed\n");
-		goto out;
+		goto out_free_pr_reg_cache;
 	}
 	t10_alua_lu_gp_mem_cache = kmem_cache_create("t10_alua_lu_gp_mem_cache",
 			sizeof(struct t10_alua_lu_gp_member),
@@ -138,7 +141,7 @@ int init_se_kmem_caches(void)
 	if (!t10_alua_lu_gp_mem_cache) {
 		pr_err("kmem_cache_create() for t10_alua_lu_gp_mem_"
 				"cache failed\n");
-		goto out;
+		goto out_free_lu_gp_cache;
 	}
 	t10_alua_tg_pt_gp_cache = kmem_cache_create("t10_alua_tg_pt_gp_cache",
 			sizeof(struct t10_alua_tg_pt_gp),
@@ -146,7 +149,7 @@ int init_se_kmem_caches(void)
 	if (!t10_alua_tg_pt_gp_cache) {
 		pr_err("kmem_cache_create() for t10_alua_tg_pt_gp_"
 				"cache failed\n");
-		goto out;
+		goto out_free_lu_gp_mem_cache;
 	}
 	t10_alua_tg_pt_gp_mem_cache = kmem_cache_create(
 			"t10_alua_tg_pt_gp_mem_cache",
@@ -156,34 +159,41 @@ int init_se_kmem_caches(void)
 	if (!t10_alua_tg_pt_gp_mem_cache) {
 		pr_err("kmem_cache_create() for t10_alua_tg_pt_gp_"
 				"mem_t failed\n");
-		goto out;
+		goto out_free_tg_pt_gp_cache;
 	}
 
+	target_completion_wq = alloc_workqueue("target_completion",
+					       WQ_MEM_RECLAIM, 0);
+	if (!target_completion_wq)
+		goto out_free_tg_pt_gp_mem_cache;
+
 	return 0;
+
+out_free_tg_pt_gp_mem_cache:
+	kmem_cache_destroy(t10_alua_tg_pt_gp_mem_cache);
+out_free_tg_pt_gp_cache:
+	kmem_cache_destroy(t10_alua_tg_pt_gp_cache);
+out_free_lu_gp_mem_cache:
+	kmem_cache_destroy(t10_alua_lu_gp_mem_cache);
+out_free_lu_gp_cache:
+	kmem_cache_destroy(t10_alua_lu_gp_cache);
+out_free_pr_reg_cache:
+	kmem_cache_destroy(t10_pr_reg_cache);
+out_free_ua_cache:
+	kmem_cache_destroy(se_ua_cache);
+out_free_sess_cache:
+	kmem_cache_destroy(se_sess_cache);
+out_free_tmr_req_cache:
+	kmem_cache_destroy(se_tmr_req_cache);
+out_free_cmd_cache:
+	kmem_cache_destroy(se_cmd_cache);
 out:
-	if (se_cmd_cache)
-		kmem_cache_destroy(se_cmd_cache);
-	if (se_tmr_req_cache)
-		kmem_cache_destroy(se_tmr_req_cache);
-	if (se_sess_cache)
-		kmem_cache_destroy(se_sess_cache);
-	if (se_ua_cache)
-		kmem_cache_destroy(se_ua_cache);
-	if (t10_pr_reg_cache)
-		kmem_cache_destroy(t10_pr_reg_cache);
-	if (t10_alua_lu_gp_cache)
-		kmem_cache_destroy(t10_alua_lu_gp_cache);
-	if (t10_alua_lu_gp_mem_cache)
-		kmem_cache_destroy(t10_alua_lu_gp_mem_cache);
-	if (t10_alua_tg_pt_gp_cache)
-		kmem_cache_destroy(t10_alua_tg_pt_gp_cache);
-	if (t10_alua_tg_pt_gp_mem_cache)
-		kmem_cache_destroy(t10_alua_tg_pt_gp_mem_cache);
 	return -ENOMEM;
 }
 
 void release_se_kmem_caches(void)
 {
+	destroy_workqueue(target_completion_wq);
 	kmem_cache_destroy(se_cmd_cache);
 	kmem_cache_destroy(se_tmr_req_cache);
 	kmem_cache_destroy(se_sess_cache);
@@ -689,6 +699,33 @@ void transport_complete_sync_cache(struct se_cmd *cmd, int good)
 }
 EXPORT_SYMBOL(transport_complete_sync_cache);
 
+static void target_complete_timeout_work(struct work_struct *work)
+{
+	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
+	unsigned long flags;
+
+	/*
+	 * Reset cmd->t_se_count to allow transport_put_cmd()
+	 * to allow last call to free memory resources.
+	 */
+	spin_lock_irqsave(&cmd->t_state_lock, flags);
+	if (atomic_read(&cmd->t_transport_timeout) > 1) {
+		int tmp = (atomic_read(&cmd->t_transport_timeout) - 1);
+
+		atomic_sub(tmp, &cmd->t_se_count);
+	}
+	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
+
+	transport_put_cmd(cmd);
+}
+
+static void target_complete_failure_work(struct work_struct *work)
+{
+	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
+
+	transport_generic_request_failure(cmd, 1, 1);
+}
+
 /*	transport_complete_task():
  *
  *	Called from interrupt and non interrupt context depending
@@ -698,7 +735,6 @@ void transport_complete_task(struct se_task *task, int success)
 {
 	struct se_cmd *cmd = task->task_se_cmd;
 	struct se_device *dev = cmd->se_dev;
-	int t_state;
 	unsigned long flags;
 #if 0
 	pr_debug("task: %p CDB: 0x%02x obj_ptr: %p\n", task,
@@ -749,17 +785,12 @@ void transport_complete_task(struct se_task *task, int success)
 	 * the processing thread.
 	 */
 	if (task->task_flags & TF_TIMEOUT) {
-		if (!atomic_dec_and_test(
-				&cmd->t_task_cdbs_timeout_left)) {
-			spin_unlock_irqrestore(&cmd->t_state_lock,
-				flags);
+		if (!atomic_dec_and_test(&cmd->t_task_cdbs_timeout_left)) {
+			spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 			return;
 		}
-		t_state = TRANSPORT_COMPLETE_TIMEOUT;
-		spin_unlock_irqrestore(&cmd->t_state_lock, flags);
-
-		transport_add_cmd_to_queue(cmd, t_state, false);
-		return;
+		INIT_WORK(&cmd->work, target_complete_timeout_work);
+		goto out_queue;
 	}
 	atomic_dec(&cmd->t_task_cdbs_timeout_left);
 
@@ -769,28 +800,29 @@ void transport_complete_task(struct se_task *task, int success)
 	 * device queue depending upon int success.
 	 */
 	if (!atomic_dec_and_test(&cmd->t_task_cdbs_left)) {
-		if (!success)
-			cmd->t_tasks_failed = 1;
-
 		spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 		return;
 	}
 
 	if (!success || cmd->t_tasks_failed) {
-		t_state = TRANSPORT_COMPLETE_FAILURE;
 		if (!task->task_error_status) {
 			task->task_error_status =
 				PYX_TRANSPORT_UNKNOWN_SAM_OPCODE;
 			cmd->transport_error_status =
 				PYX_TRANSPORT_UNKNOWN_SAM_OPCODE;
 		}
+		INIT_WORK(&cmd->work, target_complete_failure_work);
 	} else {
 		atomic_set(&cmd->t_transport_complete, 1);
-		t_state = TRANSPORT_COMPLETE_OK;
+		INIT_WORK(&cmd->work, target_complete_ok_work);
 	}
+
+out_queue:
+	cmd->t_state = TRANSPORT_COMPLETE;
+	atomic_set(&cmd->t_transport_active, 1);
 	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 
-	transport_add_cmd_to_queue(cmd, t_state, false);
+	queue_work(target_completion_wq, &cmd->work);
 }
 EXPORT_SYMBOL(transport_complete_task);
 
@@ -1642,8 +1674,6 @@ int transport_generic_allocate_tasks(
 }
 EXPORT_SYMBOL(transport_generic_allocate_tasks);
 
-static void transport_generic_request_failure(struct se_cmd *, int, int);
-
 /*
  * Used by fabric module frontends to queue tasks directly.
  * Many only be used from process context only
@@ -1985,25 +2015,6 @@ static void transport_direct_request_timeout(struct se_cmd *cmd)
 	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 }
 
-static void transport_generic_request_timeout(struct se_cmd *cmd)
-{
-	unsigned long flags;
-
-	/*
-	 * Reset cmd->t_se_count to allow transport_put_cmd()
-	 * to allow last call to free memory resources.
-	 */
-	spin_lock_irqsave(&cmd->t_state_lock, flags);
-	if (atomic_read(&cmd->t_transport_timeout) > 1) {
-		int tmp = (atomic_read(&cmd->t_transport_timeout) - 1);
-
-		atomic_sub(tmp, &cmd->t_se_count);
-	}
-	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
-
-	transport_put_cmd(cmd);
-}
-
 static inline u32 transport_lba_21(unsigned char *cdb)
 {
 	return ((cdb[1] & 0x1f) << 16) | (cdb[2] << 8) | cdb[3];
@@ -2094,10 +2105,12 @@ static void transport_task_timeout_handler(unsigned long data)
 	pr_debug("transport task: %p cmd: %p timeout ZERO t_task_cdbs_left\n",
 			task, cmd);
 
-	cmd->t_state = TRANSPORT_COMPLETE_FAILURE;
+	INIT_WORK(&cmd->work, target_complete_failure_work);
+	cmd->t_state = TRANSPORT_COMPLETE;
+	atomic_set(&cmd->t_transport_active, 1);
 	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
 
-	transport_add_cmd_to_queue(cmd, TRANSPORT_COMPLETE_FAILURE, false);
+	queue_work(target_completion_wq, &cmd->work);
 }
 
 static void transport_start_task_timer(struct se_task *task)
@@ -2879,7 +2892,7 @@ static int transport_generic_cmd_sequencer(
 		if (passthrough)
 			break;
 		/*
-		 * Setup BIDI XOR callback to be run during transport_generic_complete_ok()
+		 * Setup BIDI XOR callback to be run after I/O completion.
 		 */
 		cmd->transport_complete_callback = &transport_xor_callback;
 		cmd->t_tasks_fua = (cdb[1] & 0x8);
@@ -2913,8 +2926,8 @@ static int transport_generic_cmd_sequencer(
 				break;
 
 			/*
-			 * Setup BIDI XOR callback to be run during
-			 * transport_generic_complete_ok()
+			 * Setup BIDI XOR callback to be run during after I/O
+			 * completion.
 			 */
 			cmd->transport_complete_callback = &transport_xor_callback;
 			cmd->t_tasks_fua = (cdb[10] & 0x8);
@@ -3311,8 +3324,7 @@ out_invalid_cdb_field:
 }
 
 /*
- * Called from transport_generic_complete_ok() and
- * transport_generic_request_failure() to determine which dormant/delayed
+ * Called from I/O completion to determine which dormant/delayed
  * and ordered cmds need to have their tasks added to the execution queue.
  */
 static void transport_complete_task_attr(struct se_cmd *cmd)
@@ -3433,9 +3445,11 @@ static void transport_handle_queue_full(
 	schedule_work(&cmd->se_dev->qf_work_queue);
 }
 
-static void transport_generic_complete_ok(struct se_cmd *cmd)
+static void target_complete_ok_work(struct work_struct *work)
 {
+	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
 	int reason = 0, ret;
+
 	/*
 	 * Check if we need to move delayed/dormant tasks from cmds on the
 	 * delayed execution list after a HEAD_OF_QUEUE or ORDERED Task
@@ -4778,21 +4792,12 @@ get_cmd:
 		case TRANSPORT_PROCESS_WRITE:
 			transport_generic_process_write(cmd);
 			break;
-		case TRANSPORT_COMPLETE_OK:
-			transport_generic_complete_ok(cmd);
-			break;
 		case TRANSPORT_FREE_CMD_INTR:
 			transport_generic_free_cmd(cmd, 0);
 			break;
 		case TRANSPORT_PROCESS_TMR:
 			transport_generic_do_tmr(cmd);
 			break;
-		case TRANSPORT_COMPLETE_FAILURE:
-			transport_generic_request_failure(cmd, 1, 1);
-			break;
-		case TRANSPORT_COMPLETE_TIMEOUT:
-			transport_generic_request_timeout(cmd);
-			break;
 		case TRANSPORT_COMPLETE_QF_WP:
 			transport_write_pending_qf(cmd);
 			break;

include/target/target_core_base.h

@@ -86,9 +86,7 @@ enum transport_state_table {
 	TRANSPORT_WRITE_PENDING	= 3,
 	TRANSPORT_PROCESS_WRITE	= 4,
 	TRANSPORT_PROCESSING	= 5,
-	TRANSPORT_COMPLETE_OK	= 6,
-	TRANSPORT_COMPLETE_FAILURE = 7,
-	TRANSPORT_COMPLETE_TIMEOUT = 8,
+	TRANSPORT_COMPLETE	= 6,
 	TRANSPORT_PROCESS_TMR	= 9,
 	TRANSPORT_ISTATE_PROCESSING = 11,
 	TRANSPORT_NEW_CMD_MAP	= 16,
@@ -492,6 +490,8 @@ struct se_cmd {
 	struct completion	transport_lun_stop_comp;
 	struct scatterlist	*t_tasks_sg_chained;
 
+	struct work_struct	work;
+
 	/*
 	 * Used for pre-registered fabric SGL passthrough WRITE and READ
 	 * with the special SCF_PASSTHROUGH_CONTIG_TO_SG case for TCM_Loop