In this case d3d12_command_allocator_allocate_descriptor_set() is
only called for clearing UAVs. This helps on platforms with limited
descriptor maximum counts.
The descriptor component of struct d3d12_desc is replaced with a union
containing a pointer which can be swapped out using
InterlockedExchangePointer(). To make it safe to increment the refcount
of such an object it is necessary to cache freed objects. Elimination
of the descriptor mutexes on games which use multithreaded descriptor
writes nearly doubles framerate on recent hardware.
Eliminates vk_sets_mutex. Performance on average may be lower until
the descriptor mutexes are replaced and Vulkan writes are buffered
to reduce thunk calls.
d3d12_command_queue_flush_ops() can renter itself while processing signal
events. Since we don't use recursive mutexes, we currently have to check
some of the queue variables without holding the mutex, which is not safe.
This is solved by allowing the queue to release its mutex while it is
processing entries: when flushing, the queue is briefly locked, the
is_flushing flag is set, the queue content is copied away and the
queue is unlocked again. After having processed the entries, the
queue is locked again to check is something else was added in the
meantime. This is repeated until the queue is empty (or a wait operation
is blocking it).
This should also remove some latency when a thread pushes to the queue
while another one is processing it, but I didn't try to measure any
impact. While it is expected that with this patch the queue mutex
will be locked and unlocked more frequently, it should also remain
locked for less time, hopefully creating little contention.
