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

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Message-ID: <50AB26D2.5090602@vmware.com>
Date:	Tue, 20 Nov 2012 07:44:34 +0100
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Dave Airlie <airlied@...il.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 11/20/2012 07:19 AM, Dave Airlie wrote:
> 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.

 From VMware's side this won't be a problem, since other VMware kernel 
modules (VMCI IIRC) use RCU.

In any case I have a new version of the "vmwgfx optimization" patch 
series that mostly add documentation and
annotation (by  using a drm_ht_xxx_rcu) interface for hashtab, after an 
internal review by Dmitry Torkov. I see you've already
applied the original patch series. Do you want me to send out the new 
one or rebase it against current drm-next?

Thanks,
Thomas

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