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List: linaro-mm-sig
Subject: Re: [Linaro-mm-sig] Use dma_fence_array for implementing shared dma_resv fences
From: Daniel Vetter <daniel () ffwll ! ch>
Date: 2019-08-27 16:37:41
Message-ID: 20190827163741.GD2112 () phenom ! ffwll ! local
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On Mon, Aug 26, 2019 at 04:57:22PM +0200, Christian König wrote:
> This is the new dma_fence_array based container for shared fences in the
> dma_resv object.
>
> Advantage of this approach is that you can grab a reference to the
> current set of shared fences at any time, which allows us to drop the
> sequence number increment and makes the whole RCU handling much more
> easier.
>
> Disadvantage is that RCU users now have to grab a reference instead of
> using the sequence counter. As far as I can see i915 was actually the
> only driver doing this.
>
> So we optimize for adding more fences instead of reading them now.
>
> Another behavior change worth noting is that the shared fences are now
> only visible after unlocking the dma_resv object or calling
> dma_resv_fences_commit() manually.
I think more specific point for publishing fences makes a lot of sense, so
this sounds like a solid improvement on the dma_resv api. I'm working on
some dma_fence instrumentation where that at least might be useful.
/me back to burried state
Cheers, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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