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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>
This commit is contained in:
Nicholas Bellinger 2011-11-30 18:18:33 -08:00
parent 65586d51e0
commit 4d2300ccff
2 changed files with 24 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
drivers/target/target_core_transport.c
View File

@ -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)

1
include/target/target_core_base.h
View File

@ -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 */