Recording of command nodes into Vulkan command buffers is very easily parallelisable as it can effectively be treated as part of the GPU execution, which is inherently async. By moving it to a seperate thread we can shave off about 20% of GPFIFO execution time. It should be noted that the command scheduler command buffer infra is no longer used, since we need to record texture updates on the GPFIFO thread (while another slot is being recorded on the record thread) and then use the same command buffer on the record thread later. This ends up requiring a pool per slot, which is reasonable considering we only have four slots by default.
Using command executor for each state individual update was found to be infeasible due to the shear number of state updates per draw and it relying on per-node heap allocations. Instead this commit takes advantage of each state update being used only once to implement a system of linearly-allocated state update commands that are linked together. After setting up all draw state with StateUpdateBuilder, the built StateUpdater can then be used in the execution phase to record all of the draw state into the command buffer with almost zero ovehead.
SMO implements instanced draws by repeating the same draw just with a different constant buffer bound. Reduce the cost of this significantly by detecting such cases and instead of processing every descriptor, copy the previous descriptor set and update only the ones affected by the bound constant buffer.
Credits to ripinperiperi for the initial idea and making me aware of how SMO does these draws
When a buffer is trapped nearly every frame, the cost of trapping and synchronising its contents starts to quickly add up. By always using the megabuffer when this is the case, since megabuffer copies are done directly from the guest, we skip the need to synchronise/trap the backing.
The original intention was to cache on the user side, but especially with shader constant buffers that's difficult and costly. Instead we can cache on the buffer side, with a page-table like structure to hold variable sized allocations indexed by the aligned view base address. This avoids most redundant copies from repeated use of the same buffer without updates inbetween.
Avoids the need to hash PipelineState when we can guess the pipeline that will be used next. This could very easily be optimised in the future with generational, usage-based caching if necessary.
gm20b performs instanced draws by repeating draw methods for each instance, the code to detect this together with the cost of interpreting macros took up around 6% of GPFIFO time in Metro Kingdom. By detecting these specific macros and performing an instanced draw directly much of that cost can be avoided.
gpu-new will use a monolithic pipeline object for each pipeline to store state, keyed by the PackedPipelineState contents. This allows for a greater level of per-pipeline optimisations and a reduction in the overall number of lookups in a draw compared to the previous system.
