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: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 7c2def7..46e2511 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -68,7 +68,7 @@
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 @@
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 @@
__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 @@
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 @@
*
* 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 @@
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 @@
transport_generic_request_failure(cmd);
}
+ new_cmd = NULL;
goto check_depth;
return 0;
@@ -4647,7 +4655,7 @@
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)