nx2: read GPU-written command lists from copies instead of draining

The trees fix (#52) drains the split and flushes for every command list
on a GPU-written page: in a Mario Kart World race ~13,500 lists and ~400
GPU round trips a second, during which the back has nothing to do. The
replay ran at ~40 fps instead of ~45.

The front now marks the pages those lists are on. The buffer cache notes
writes to them; after a compute dispatch or DMA copy that writes one it
copies the page into host memory and submits. The front waits for the
back only up to the last compute or copy work it sent (not everything
queued), then reads the copy once the GPU is done with it.

Pages the GPU wrote once, long before, and the CPU now writes lists to
have no copy: their first list drains and flushes the whole page, which
is then read from guest memory until GPU work writes it again. CPU
writes and inline uploads reach guest memory, so they keep such a page
synced but make a copy stale. A page a draw writes always drains.

Mario Kart World time-trial replay, Radeon 780M: ~40 -> ~45 fps, trees
drawn, no list drains left.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/video_core/renderer_vulkan/vk_rasterizer.h b/src/video_core/renderer_vulkan/vk_rasterizer.h
index fc282fbe8d..dbb6ebdca8 100644
--- a/src/video_core/renderer_vulkan/vk_rasterizer.h
+++ b/src/video_core/renderer_vulkan/vk_rasterizer.h
@@ -99,6 +99,8 @@ public:
     void FlushAll() override;
     void FlushRegion(DAddr addr, u64 size,
                      VideoCommon::CacheType which = VideoCommon::CacheType::All) override;
+    GpuWrittenList ReadGpuWrittenCommandList(DAddr addr, std::span<u8> out) override;
+    void NoteGpuWrittenCommandListSynced(DAddr page) override;
     bool MustFlushRegion(DAddr addr, u64 size,
                          VideoCommon::CacheType which = VideoCommon::CacheType::All) override;
     VideoCore::RasterizerDownloadArea GetFlushArea(DAddr addr, u64 size) override;
@@ -165,6 +167,10 @@ private:
 
     void FlushWork();
 
+    /// Records the copies of the command list pages the work just recorded wrote and submits, so
+    /// the GPU makes them now (BufferCache::Nx2CopyListPages).
+    void SubmitNx2ListCopies();
+
     void UpdateDynamicStates();
 
     void HandleTransformFeedback();