linux-kernel - Re: [PATCH] gpu: drm: amd: amdkfd: Remove create

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Date:	Thu, 26 May 2016 14:50:29 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Cc:	oded.gabbay@...il.com, alexander.deucher@....com,
	christian.koenig@....com, airlied@...ux.ie,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpu: drm: amd: amdkfd: Remove create_workqueue()

On Fri, May 27, 2016 at 12:15:17AM +0530, Bhaktipriya Shridhar wrote:
> alloc_workqueue replaces deprecated create_workqueue().
> 
> kfd_process_wq is used for delay destruction. A work item embedded in
> kfd_process gets queued to kfd_process_wq and when it executes it
> destroys and frees the containing kfd_process and thus itself.
> 
> This requires a dedicated workqueue because a work item once queued, may
> get freed at any point of time and any external entity cannot
> flush the work item. So, in order to wait for such a work item,
> it needs to be put on a dedicated workqueue.
> 
> kfd_module_exit() calls kfd_process_destroy_wq which ensures that all
> pending work items are finished before the module is removed.
> 
> flush_workqueue is unnecessary since destroy_workqueue() itself calls
> drain_workqueue() which flushes repeatedly till the workqueue becomes empty.
> 
> Hence flush_workqueue has been removed.

create_workqueue(NAME) maps to alloc_workqueue(NAME, WQ_MEM_RECLAIM, 1),
so the change is effectively dropping WQ_MEM_RECLAIM and changing
concurrency value from 1 to WQ_DFL_ACTIVE.  It'd be nice to explain
why these changes are safe and I think they're. It just needs
explanations.

> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>

Other than that, Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun