V4L2 video decoder buffer fence

[Nicolas Dufresne]

Le mar. 12 janv. 2021 02 h 15, Bing Song <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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