On 10/26/23 21:25, Alex Goins wrote: > On Thu, 26 Oct 2023, Sebastian Wick wrote: >> On Thu, Oct 26, 2023 at 11:57:47AM +0300, Pekka Paalanen wrote: >>> On Wed, 25 Oct 2023 15:16:08 -0500 (CDT) >>> Alex Goins <agoins@xxxxxxxxxx> wrote: >>> >>>> Despite being programmable, the LUTs are updated in a manner that is less >>>> efficient as compared to e.g. the non-static "degamma" LUT. Would it be helpful >>>> if there was some way to tag operations according to their performance, >>>> for example so that clients can prefer a high performance one when they >>>> intend to do an animated transition? I recall from the XDC HDR workshop >>>> that this is also an issue with AMD's 3DLUT, where updates can be too >>>> slow to animate. >>> >>> I can certainly see such information being useful, but then we need to >>> somehow quantize the performance. > > Right, which wouldn't even necessarily be universal, could depend on the given > host, GPU, etc. It could just be a relative performance indication, to give an > order of preference. That wouldn't tell you if it can or can't be animated, but > when choosing between two LUTs to animate you could prefer the higher > performance one. > >>> >>> What I was left puzzled about after the XDC workshop is that is it >>> possible to pre-load configurations in the background (slow), and then >>> quickly switch between them? Hardware-wise I mean. > > This works fine for our "fast" LUTs, you just point them to a surface in video > memory and they flip to it. You could keep multiple surfaces around and flip > between them without having to reprogram them in software. We can easily do that > with enumerated curves, populating them when the driver initializes instead of > waiting for the client to request them. You can even point multiple hardware > LUTs to the same video memory surface, if they need the same curve. > >> >> We could define that pipelines with a lower ID are to be preferred over >> higher IDs. > > Sure, but this isn't just an issue with a pipeline as a whole, but the > individual elements within it and how to use them in a given context. > >> >> The issue is that if programming a pipeline becomes too slow to be >> useful it probably should just not be made available to user space. > > It's not that programming the pipeline is overall too slow. The LUTs we have > that are relatively slow to program are meant to be set infrequently, or even > just once, to allow the scaler and tone mapping operator to operate in fixed > point PQ space. You might still want the tone mapper, so you would choose a > pipeline that includes them, but when it comes to e.g. animating a night light, > you would want to choose a different LUT for that purpose. > >> >> The prepare-commit idea for blob properties would help to make the >> pipelines usable again, but until then it's probably a good idea to just >> not expose those pipelines. > > The prepare-commit idea actually wouldn't work for these LUTs, because they are > programmed using methods instead of pointing them to a surface. I'm actually not > sure how slow it actually is, would need to benchmark it. I think not exposing > them at all would be overkill, since it would mean you can't use the preblending > scaler or tonemapper, and animation isn't necessary for that. > > The AMD 3DLUT is another example of a LUT that is slow to update, and it would > obviously be a major loss if that wasn't exposed. There just needs to be some > way for clients to know if they are going to kill performance by trying to > change it every frame. Might a first step be to require the ALLOW_MODESET flag to be set when changing the values for a colorop which is too slow to be updated per refresh cycle? This would tell the compositor: You can use this colorop, but you can't change its values on the fly. -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and Xwayland developer
