Readback buffers are allocated when the readback is recorded rather than on the render thread,
so only the thread that records frames touches VMA. The allocator is created externally
synchronized, and VMA is built with no-op mutexes and plain counters instead of std::mutex and
std::atomic.
Headless runs Vulkan offscreen in builds without SDL too, and CI runs the headless tests on
lavapipe, skipping the pixel tests a hardware backend doesn't match the software references on.
sleep_ms and sleep_us go, with the thread manager test waiting on an event instead, and so does
the unused portable-file-dialogs header.
The core and the headless tools no longer use mutexes, condition variables,
spinlocks, std::atomic, std::thread or volatile flags. Threads hand off through
libretro-common's retro_atomic and rthreads plus a few small pieces on top of
them in Common/Thread: Thread, MpscQueue, EventCounter, ParkingLot waits and
ReaderGate. Every wait blocks until it's woken; nothing polls on a timer.
State that only one thread touches just loses its lock. The PSP filesystem,
sceIo and the savedata dialog now belong to the emulation thread: async reads
and writes run when they're queued and complete later in emulated time, and
the IO and savedata threads are gone. The friend finder only talks to the
adhoc server and hands what it gets to the emulation thread. GPU init always
runs on the thread that starts the game.
The Vulkan render and compile queues, pipeline and render pass caches, delete
list and SPIR-V cache, the GL render queue, the software renderer's jit caches,
the file loader caches, the web debugger, UPnP, input, savestates, logging and
the GE debugger all hand off through queues and atomics. The IR jit's spinning
profiler thread goes.
A CPU thread with nothing to run now sleeps until work is queued instead of
spinning. Headless with --debugger waits for a client while stopped, and ends
the run once every client that connected has left. Web server shutdown keeps
servicing the CPU queue until the server has finished.
This extension is not available on Android, there they have
VK_GOOGLE_display_timing, which they also have an abstraction library
for, so will look at that later.
Early part of work on #17685
Multi-threaded rendering is good for smoothing out performance spikes
and increasing performance on low-power devices. However, the way we use
it it doesn't benefit latency (input lag) at all, rather the opposite.
So make it an option.
libretroadmin