linux-kernel - Re: [RFC 0/5] rework fences on struct sync_file

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Message-ID: <576D4032.3000001@vodafone.de>
Date:	Fri, 24 Jun 2016 16:14:10 +0200
From:	Christian König <deathsimple@...afone.de>
To:	Gustavo Padovan <gustavo@...ovan.org>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, marcheu@...gle.com,
	Daniel Stone <daniels@...labora.com>, seanpaul@...gle.com,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, laurent.pinchart@...asonboard.com,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>, m.chehab@...sung.com
Subject: Re: [RFC 0/5] rework fences on struct sync_file

Am 24.06.2016 um 15:17 schrieb Gustavo Padovan:
> Hi Christian,
>
> 2016-06-24 Christian König <christian.koenig@....com>:
>
>> Am 23.06.2016 um 17:29 schrieb Gustavo Padovan:
>>> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
>>>
>>> Hi all,
>>>
>>> This is an attempt to improve fence support on Sync File. The basic idea
>>> is to have only sync_file->fence and store all fences there, either as
>>> normal fences or fence_arrays. That way we can remove some potential
>>> duplication when using fence_array with sync_file: the duplication of the array
>>> of fences and the duplication of fence_add_callback() for all fences.
>>>
>>> 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 that sync_file. If
>>> there is more than one fence a fence_array is created. One important 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 by fence_array.
>>>
>>> Two fence ops had to be created to help abstract the difference between handling
>>> fences and fences_arrays: .teardown() and .get_fences(). The former 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_array).
> Are you refering only to .get_fences()?

That comment was only for the get_fences() operation, but the teardown() 
callback looks very suspicious to me as well.

Can you explain once more why that should be necessary?

Regards,
Christian.

>
>> What you should do is try to cast the fence in your sync file using
>> to_fence_array() and then you can access the fences in the array.
> Yes, that seems a better idea I think. The initial idea was to abstract
> the difference as much as possible, but it doesn't seem really worth
> for .get_fences().
>
> 	Gustavo
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