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[PATCH] [media] tc358743: Remove deprecated create_singlethread_workqueue

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  [PATCH] [media] tc358743: Remove deprecated  create_singlethread_workqueue Bhaktipriya Shridhar <bhaktipriya96@gmail.com> - 2016-07-02 12:50 +0200
    Re: [PATCH] [media] tc358743: Remove deprecated  create_singlethread_workqueue Tejun Heo <tj@kernel.org> - 2016-07-02 15:50 +0200

#1435787 — [PATCH] [media] tc358743: Remove deprecated create_singlethread_workqueue

The workqueue "work_queues" enables hotplugging.
It has a single work item(&state->delayed_work_enable_hotplug) and hence
doesn't require ordering. Also, it is not being used on a memory
reclaim path. Hence, the singlethreaded workqueue has been replaced with
the use of system_wq.

System workqueues have been able to handle high level of concurrency
for a long time now and hence it's not required to have a singlethreaded
workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
created with create_singlethread_workqueue(), system_wq allows multiple
work items to overlap executions even on the same CPU; however, a
per-cpu workqueue doesn't have any CPU locality or global ordering
guarantee unless the target CPU is explicitly specified and thus the
increase of local concurrency shouldn't make any difference.

Work item has been sync cancelled in tc358743_remove() to ensure
that there are no pending tasks while disconnecting the driver.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
---
 drivers/media/i2c/tc358743.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

diff --git a/drivers/media/i2c/tc358743.c b/drivers/media/i2c/tc358743.c
index 6cf6d06..1e3a0dd 100644
--- a/drivers/media/i2c/tc358743.c
+++ b/drivers/media/i2c/tc358743.c
@@ -89,8 +89,6 @@ struct tc358743_state {
 	struct v4l2_ctrl *audio_sampling_rate_ctrl;
 	struct v4l2_ctrl *audio_present_ctrl;

-	/* work queues */
-	struct workqueue_struct *work_queues;
 	struct delayed_work delayed_work_enable_hotplug;

 	/* edid  */
@@ -425,8 +423,7 @@ static void tc358743_enable_edid(struct v4l2_subdev *sd)

 	/* Enable hotplug after 100 ms. DDC access to EDID is also enabled when
 	 * hotplug is enabled. See register DDC_CTL */
-	queue_delayed_work(state->work_queues,
-			   &state->delayed_work_enable_hotplug, HZ / 10);
+	schedule_delayed_work(&state->delayed_work_enable_hotplug, HZ / 10);

 	tc358743_enable_interrupts(sd, true);
 	tc358743_s_ctrl_detect_tx_5v(sd);
@@ -1884,14 +1881,6 @@ static int tc358743_probe(struct i2c_client *client,
 		goto err_hdl;
 	}

-	/* work queues */
-	state->work_queues = create_singlethread_workqueue(client->name);
-	if (!state->work_queues) {
-		v4l2_err(sd, "Could not create work queue\n");
-		err = -ENOMEM;
-		goto err_hdl;
-	}
-
 	state->pad.flags = MEDIA_PAD_FL_SOURCE;
 	err = media_entity_pads_init(&sd->entity, 1, &state->pad);
 	if (err < 0)
@@ -1940,7 +1929,6 @@ static int tc358743_probe(struct i2c_client *client,

 err_work_queues:
 	cancel_delayed_work(&state->delayed_work_enable_hotplug);
-	destroy_workqueue(state->work_queues);
 	mutex_destroy(&state->confctl_mutex);
 err_hdl:
 	media_entity_cleanup(&sd->entity);
@@ -1954,7 +1942,6 @@ static int tc358743_remove(struct i2c_client *client)
 	struct tc358743_state *state = to_state(sd);

 	cancel_delayed_work(&state->delayed_work_enable_hotplug);
-	destroy_workqueue(state->work_queues);
 	v4l2_async_unregister_subdev(sd);
 	v4l2_device_unregister_subdev(sd);
 	mutex_destroy(&state->confctl_mutex);
--
2.1.4

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#1435828

On Sat, Jul 02, 2016 at 04:11:53PM +0530, Bhaktipriya Shridhar wrote:
> The workqueue "work_queues" enables hotplugging.
> It has a single work item(&state->delayed_work_enable_hotplug) and hence
> doesn't require ordering. Also, it is not being used on a memory
> reclaim path. Hence, the singlethreaded workqueue has been replaced with
> the use of system_wq.
> 
> System workqueues have been able to handle high level of concurrency
> for a long time now and hence it's not required to have a singlethreaded
> workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
> created with create_singlethread_workqueue(), system_wq allows multiple
> work items to overlap executions even on the same CPU; however, a
> per-cpu workqueue doesn't have any CPU locality or global ordering
> guarantee unless the target CPU is explicitly specified and thus the
> increase of local concurrency shouldn't make any difference.
> 
> Work item has been sync cancelled in tc358743_remove() to ensure
> that there are no pending tasks while disconnecting the driver.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

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