Re: [PATCH] USB: appledisplay: Remove deprecated create_singlethread_workqueue

From: Tejun Heo
Date: Tue Jul 26 2016 - 11:36:26 EST

On Tue, Jul 26, 2016 at 11:11:18AM +0530, Bhaktipriya Shridhar wrote:
> The workqueue "wq" is involved in controlling the brightness of an
> Apple Cinema Display over USB.
> It has a single work item(&pdata->work) per appledisplay 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.
> The work item is self-requeueing and needs to wait for the in-flight
> work item to finish before proceeding with destruction.
> Hence, it has been sync cancelled in appledisplay_disconnect().
> This also ensures that there are no pending tasks while disconnecting the
> driver.
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@xxxxxxxxx>
> @@ -159,7 +158,7 @@ static int appledisplay_bl_update_status(struct backlight_device *bd)
> pdata->msgdata, 2,
> mutex_unlock(&pdata->sysfslock);
> -
> +


Other than that,

Acked-by: Tejun Heo <tj@xxxxxxxxxx>