[Mesa-dev] 10bit HEVC decoding for RadeonSI v2

[Christian König]

Hi Rainer,

the render thread doesn't wait either.

See when you dispatch some work the AMD drivers always wait for 
prerequisites in the background, not in the foreground.

The older radeon driver uses hardware semaphores for this while amdgpu 
has a GPU scheduler which handles that stuff.

This is very important because when you hold back rendering work in the 
application the driver stack won't know about it and power management 
starts to stutter.

Not so important for 1920p because power management should be able to 
compensate the work peaks, but for 4K that's something mandatory to let 
the driver be able to estimate future load.

We even discussed in our multimedia meeting if we shouldn't limit 3D 
power management when UVD/VCN decoding is active because of that 
problem. But I'm not very keen about those workarounds because it's 
really counterproductive for transcode use cases to have the 3D engine 
idling around with high clocks.

Regards,
Christian.

Am 11.02.2018 um 12:51 schrieb rainer.hochecker at onlinehome.de:
> Hi Christian,
> For Kodi it is better to wait on the thread that does decoding than later
> by the render thread. Means it is desired to call it.
> Does vaSyncSurface block as stated by the docs?
> Regards,
> Rainer
> *Gesendet:* Sonntag, 11. Februar 2018 um 11:02 Uhr
> *Von:* "Christian König" <christian.koenig at amd.com>
> *An:* "Philipp Kerling" <pkerling at casix.org>, sw at jkqxz.net
> *Cc:* rainer.hochecker at onlinehome.de, peter.fruehberger at gmail.com, 
> michel at daenzer.net, mesa-dev at lists.freedesktop.org, 
> harry.wentland at amd.com, lrusak at libreelec.tv
> *Betreff:* Re: [Mesa-dev] 10bit HEVC decoding for RadeonSI v2
> Am 09.02.2018 um 21:35 schrieb Philipp Kerling:
> > Hi,
> >
> > resurrecting this thread again since there's been some progress on the
> > Kodi side.
> >
> >> For the EGL part, see <https://github.com/01org/libva/pull/125>
> >> and 
> <https://lists.freedesktop.org/archives/mesa-dev/2017-October/171246.html>.
> > We recently started testing vaExportSurfaceHandle support, so we will
> > have this covered soon.
> >
> >> I have been testing with mpv and ffmpeg; any thoughts from the
> >> Kodi point of view would be most welcome.
> > It generally works quite well, but we still have the unresolved
> > vaSyncSurface problem.
> > To recap: vaExportSurfaceHandle requires calling vaSyncSurface to make
> > sure that the decode is actually finished and the buffer is usable
> > before rendering the frame. However, vaSyncSurface was largely
> > unimplemented on mesa back then and it was unclear how to proceed with
> > regard to decode (VAAPI)/present (EGL+GL) synchronization.
> >
> > So on to the question: Is this still the case, or has there been
> > progress on implementing vaSyncSurface in mesa? In either case, do we
> > need that support or does this syncing work implicitly somehow on AMD?
> >
> > I've noticed that mpv does not seem to call vaSyncSurface, although it
> > technically should.
>
> Actually the mpv approach is correct.
>
> Calling vaSyncSurface is unnecessary and undesired for AMD hardware
> because it moves synchronization to the CPU while it should happen on
> the GPU and/or GPU scheduler.
>
> E.g. our 3D pipeline can wait for hardware video decoding to finish
> before starting the rendering. We even have some implementations which
> allow the 3D pipeline to start when only the first halve of the picture
> is decoded etc..
>
> If we don't do this the 3D pipeline runs dry between frame decoding
> which leads to problems with power management.
>
> We should probably add a flag or bit or feature or something like this
> to note that the application explicitly should NOT call vaSyncSurface
> before exporting the surface.
>
> Regards,
> Christian.
>
> >
> > Best regards,
> > Philipp
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev

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