linux-kernel - Re: [PATCH 3/4] drm/ttm, drm/vmwgfx: Use RCU locking for object lookups v3

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Message-ID: <CAPM=9txb2aQ6zXYKdxDiuL0jOBA9epM_kBT8zeOOcUDN42gQ_w@mail.gmail.com>
Date:	Tue, 20 Nov 2012 16:19:25 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	airlied@...hat.com, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] drm/ttm, drm/vmwgfx: Use RCU locking for object
 lookups v3

On Tue, Nov 6, 2012 at 9:31 PM, Thomas Hellstrom <thellstrom@...are.com> wrote:
> The mostly used lookup+get put+potential_destroy path of TTM objects
> is converted to use RCU locks. This will substantially decrease the amount
> of locked bus cycles during normal operation.
> Since we use kfree_rcu to free the objects, no rcu synchronization is needed
> at module unload time.

As this is the first use of RCU in a drm driver from what I can see,
let me remind that the
RCU patent agreement AFAIK only covers GPL works.

So non-GPL or other OSes porting this code should take not of this.

Dave.
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