[EXT] Re: V4L2 video decoder buffer fence

[Bing Song]

For video decoder output buffer, it can’t use out fence as video decoder output buffer reording. Video decoder output buffer can use input fence which from gl-render in Weston. Can this use case improve performance?

Regards,
Bing

From: gstreamer-devel <gstreamer-devel-bounces at lists.freedesktop.org> On Behalf Of Nicolas Dufresne
Sent: 2021年1月12日 22:19
To: Discussion of the development of and with GStreamer <gstreamer-devel at lists.freedesktop.org>
Subject: [EXT] Re: V4L2 video decoder buffer fence


Caution: EXT Email

Le mar. 12 janv. 2021 02 h 15, Bing Song <bing.song at nxp.com<mailto:bing.song at nxp.com>> a écrit :
Hi,

I want to implement v4l2 video decoder buffer fence. But I don’t know why it can benefit performance? Video HW decoder is one step decode. We use Hantro video decoder. CPU SW will parser SPS/PPS and slice header. HW will decode video frame within one step decode. How dma buf fence can benefit decode performance?

Fences alone don't save in performance. You need to combine these fences with a GPU or a display driver API to actually gain.

Fences in GPU and display driver are used to parallelize the processing without using extra threads, so without the context switch cost.

With the fences, the driver can deliver incomplete frames and program the next job without blocking. This is equivalent to adding a render delay of 1 frame, but without the full frame latency.

Note that fences are not yet supported in V4L2 API, there was a proposal but with some limitations (ordering and timestamp related).


Regards,
Bing
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