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Commit 4d2300cc authored by Nicholas Bellinger's avatar Nicholas Bellinger
Browse files

target: Remove extra se_device->execute_task_lock access in fast path 



This patch makes __transport_execute_tasks() perform the addition of
tasks to dev->execute_task_list via __transport_add_tasks_from_cmd()
while holding dev->execute_task_lock during normal I/O fast path
submission.

It effectively removes the unnecessary re-acquire of dev->execute_task_lock
during transport_execute_tasks() -> transport_add_tasks_from_cmd() ahead
of calling  __transport_execute_tasks() to queue tasks for the passed
*se_cmd descriptor.

(v2: Re-add goto check_depth usage for multi-task submission for now..)

Cc: Christoph Hellwig <hch@lst.de>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Joern Engel <joern@logfs.org>
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent 65586d51

drivers/target/target_core_transport.c

+24 −16
Original line number Diff line number Diff line
@@ -68,7 +68,7 @@ struct kmem_cache *t10_alua_tg_pt_gp_mem_cache; 


static int transport_generic_write_pending(struct se_cmd *);

static int transport_processing_thread(void *param);

static int __transport_execute_tasks(struct se_device *dev);

static int __transport_execute_tasks(struct se_device *dev, struct se_cmd *);

static void transport_complete_task_attr(struct se_cmd *cmd);

static void transport_handle_queue_full(struct se_cmd *cmd,

		struct se_device *dev);
@@ -851,13 +851,11 @@ static void transport_add_tasks_to_state_queue(struct se_cmd *cmd) 
	spin_unlock_irqrestore(&cmd->t_state_lock, flags);

}



static void transport_add_tasks_from_cmd(struct se_cmd *cmd)

static void __transport_add_tasks_from_cmd(struct se_cmd *cmd)

{

	struct se_device *dev = cmd->se_dev;

	struct se_task *task, *task_prev = NULL;

	unsigned long flags;



	spin_lock_irqsave(&dev->execute_task_lock, flags);

	list_for_each_entry(task, &cmd->t_task_list, t_list) {

		if (!list_empty(&task->t_execute_list))

			continue;
@@ -868,6 +866,15 @@ static void transport_add_tasks_from_cmd(struct se_cmd *cmd) 
		__transport_add_task_to_execute_queue(task, task_prev, dev);

		task_prev = task;

	}

}



static void transport_add_tasks_from_cmd(struct se_cmd *cmd)

{

	unsigned long flags;

	struct se_device *dev = cmd->se_dev;



	spin_lock_irqsave(&dev->execute_task_lock, flags);

	__transport_add_tasks_from_cmd(cmd);

	spin_unlock_irqrestore(&dev->execute_task_lock, flags);

}
@@ -2075,19 +2082,16 @@ static int transport_execute_tasks(struct se_cmd *cmd) 
		if (!add_tasks)

			goto execute_tasks;

		/*

		 * This calls transport_add_tasks_from_cmd() to handle

		 * HEAD_OF_QUEUE ordering for SAM Task Attribute emulation

		 * (if enabled) in __transport_add_task_to_execute_queue() and

		 * transport_add_task_check_sam_attr().

		 * __transport_execute_tasks() -> __transport_add_tasks_from_cmd()

		 * adds associated se_tasks while holding dev->execute_task_lock

		 * before I/O dispath to avoid a double spinlock access.

		 */

		transport_add_tasks_from_cmd(cmd);

		__transport_execute_tasks(se_dev, cmd);

		return 0;

	}

	/*

	 * Kick the execution queue for the cmd associated struct se_device

	 * storage object.

	 */



execute_tasks:

	__transport_execute_tasks(se_dev);

	__transport_execute_tasks(se_dev, NULL);

	return 0;

}
@@ -2097,7 +2101,7 @@ static int transport_execute_tasks(struct se_cmd *cmd) 
 *

 * Called from transport_processing_thread()

 */

static int __transport_execute_tasks(struct se_device *dev)

static int __transport_execute_tasks(struct se_device *dev, struct se_cmd *new_cmd)

{

	int error;

	struct se_cmd *cmd = NULL;
@@ -2106,6 +2110,9 @@ static int __transport_execute_tasks(struct se_device *dev) 


check_depth:

	spin_lock_irq(&dev->execute_task_lock);

	if (new_cmd != NULL)

		__transport_add_tasks_from_cmd(new_cmd);



	if (list_empty(&dev->execute_task_list)) {

		spin_unlock_irq(&dev->execute_task_lock);

		return 0;
@@ -2139,6 +2146,7 @@ static int __transport_execute_tasks(struct se_device *dev) 
		transport_generic_request_failure(cmd);

	}



	new_cmd = NULL;

	goto check_depth;



	return 0;
@@ -4647,7 +4655,7 @@ static int transport_processing_thread(void *param) 
			goto out;



get_cmd:

		__transport_execute_tasks(dev);

		__transport_execute_tasks(dev, NULL);



		cmd = transport_get_cmd_from_queue(&dev->dev_queue_obj);

		if (!cmd)

include/target/target_core_base.h

+0 −1
Original line number Diff line number Diff line
@@ -781,7 +781,6 @@ struct se_device { 
	u32			dev_port_count;

	/* See transport_device_status_table */

	u32			dev_status;

	u32			dev_tcq_window_closed;

	/* Physical device queue depth */

	u32			queue_depth;

	/* Used for SPC-2 reservations enforce of ISIDs */