From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gustavo Padovan <gustavo.padovan@collabora.com>
Subject: Re: [RFC 0/5] rework fences on struct sync_file
Date: Fri, 24 Jun 2016 11:59:33 -0300
Message-ID: <20160624145933.GF2508@joana>
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To: Christian =?iso-8859-1?Q?K=F6nig?= <deathsimple@vodafone.de>
Cc: Gustavo Padovan <gustavo@padovan.org>, Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, dri-devel@lists.freedesktop.org, marcheu@google.com, Daniel Stone <daniels@collabora.com>, seanpaul@google.com, Daniel Vetter <daniel.vetter@ffwll.ch>, linux-kernel@vger.kernel.org, laurent.pinchart@ideasonboard.com, Gustavo Padovan <gustavo.padovan@collabora.co.uk>, John Harrison <John.C.Harrison@Intel.com>, m.chehab@samsung.com
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2016-06-24 Christian K=F6nig <deathsimple@vodafone.de>:

> Am 24.06.2016 um 15:17 schrieb Gustavo Padovan:
> > Hi Christian,
> >=20
> > 2016-06-24 Christian K=F6nig <christian.koenig@amd.com>:
> >=20
> > > Am 23.06.2016 um 17:29 schrieb Gustavo Padovan:
> > > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > >=20
> > > > Hi all,
> > > >=20
> > > > This is an attempt to improve fence support on Sync File. The b=
asic idea
> > > > is to have only sync_file->fence and store all fences there, ei=
ther as
> > > > normal fences or fence_arrays. That way we can remove some pote=
ntial
> > > > duplication when using fence_array with sync_file: the duplicat=
ion of the array
> > > > of fences and the duplication of fence_add_callback() for all f=
ences.
> > > >=20
> > > > Now when creating a new sync_file during the merge process sync=
_file_set_fence()
> > > > will set sync_file->fence based on the number of fences for tha=
t sync_file. If
> > > > there is more than one fence a fence_array is created. One impo=
rtant advantage
> > > > approach is that we only add one fence callback now, no matter =
how many fences
> > > > there are in a sync_file - the individual callbacks are added b=
y fence_array.
> > > >=20
> > > > Two fence ops had to be created to help abstract the difference=
 between handling
> > > > fences and fences_arrays: .teardown() and .get_fences(). The fo=
rmer run needed
> > > > on fence_array, and the latter just return a copy of all fences=
 in the fence.
> > > > I'm not so sure about adding those two, speacially .get_fences(=
). What do you
> > > > think?
> > > Clearly not a good idea to add this a fence ops, cause those are =
specialized
> > > functions for only a certain fence implementation (the fence_arra=
y).
> > Are you refering only to .get_fences()?
>=20
> That comment was only for the get_fences() operation, but the teardow=
n()
> callback looks very suspicious to me as well.
>=20
> Can you explain once more why that should be necessary?

When the sync_file owner exits we need to clean up it and that means re=
leasing
the fence too, however with fence_array we can't just call fence_put()
as a extra reference to array->base for each fence is held when enablin=
g
signalling. Thus we need a prior step, that I called teardown(), to
remove the callback for not signaled fences and put the extra
references.

Another way to do this would be:

	if (fence_is_array(sync_file->fence))
		fence_array_destroy(to_fence_array(sync_file->fence));
	else
		fence_put(sync_file_fence);

This would avoid the extra ops, maybe we should go this way.

	Gustavo