linux-kernel - Re: [PATCH] mmc: rtsx: Remove deprecated create_singlethread

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Date:	Tue, 26 Jul 2016 13:02:12 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: rtsx: Remove deprecated
 create_singlethread_workqueue

On Tue, Jul 26, 2016 at 10:31:06PM +0530, Bhaktipriya Shridhar wrote:
> The workqueue "workq" provides support for sd/mmc async request, which
> makes next request do dma_map_sg() while previous request transferring
> data.
> 
> The workqueue has a single workitem(&host->work) 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 flushed in rtsx_pci_sdmmc_drv_remove() to ensure that
> there are no pending tasks while disconnecting the driver.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>

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

Thanks.

-- 
tejun