linux-kernel - Re: [Xen-devel] [PATCH v2] xen: xen-pciback: Remove create

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Date:	Wed, 1 Jun 2016 15:53:09 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"Juergen Gross" <jgross@...e.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Jan Beulich" <JBeulich@...e.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Doug Goldstein <cardoe@...doe.com>
CC:	Tejun Heo <tj@...nel.org>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v2] xen: xen-pciback: Remove create_workqueue

On 01/06/16 15:15, Bhaktipriya Shridhar wrote:
> System workqueues have been able to handle high level of concurrency
> for a long time now and there's no reason to use dedicated workqueues
> just to gain concurrency.  Replace dedicated xen_pcibk_wq with the
> use of system_wq.
> 
> Unlike a dedicated per-cpu workqueue created with create_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 guarantees unless the target CPU is
> explicitly specified and thus the increase of local concurrency shouldn't
> make any difference.
> 
> Since the work items could be pending, flush_work() has been used in
> xen_pcibk_disconnect(). xen_pcibk_xenbus_remove() calls free_pdev()
> which in turn calls xen_pcibk_disconnect() for every pdev to ensure that
> there is no pending task while disconnecting the driver.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
> ---
>  Changes in v2:
> 	-Changed cancel_work_sync to flush_work
> 	-Changed commit description
> 
>  Feedback to update a comment was received in v1 from David Vrabel. It has not
>  be included in v2 since some clarification was required. Will include it in
>  v3 once the details about the content and the placement of the comment are
>  received.

The comment needed updating iff this continued to use cancel_work_sync()
but since it's using flush_work() the comment is fine.

David