[buffer_cache] Simplify GPU fence synchronization and remove GPU buffer readback (#4477)

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-------------------

This is understood to improve GPU synchronization within the buffer cache in certain edge cases.

GPU Fence Strict is no longer necessary. We now apply the stronger synchronization only in the specific case that actually requires it.

The GPU Buffer Readback has been removed, as it is no longer needed following PR #4473.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4477
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

2 files changed, 20 insertions, 23 deletions

diff --git a/src/video_core/buffer_cache/buffer_cache.h b/src/video_core/buffer_cache/buffer_cache.h
index 576f20c4e7..9a5d6f322a 100644
--- a/src/video_core/buffer_cache/buffer_cache.h
+++ b/src/video_core/buffer_cache/buffer_cache.h
@@ -249,6 +249,10 @@ bool BufferCache<P>::DMACopy(GPUVAddr src_address, GPUVAddr dest_address, u64 am
     runtime.CopyBuffer(dest_buffer, src_buffer, copies, true);
     if (has_new_downloads) {
         memory_tracker.MarkRegionAsGpuModified(*cpu_dest_address, amount);
+        const bool should_sync = Settings::IsGPUFenceBehaviorBalanced() || Settings::IsGPUFenceBehaviorAccurate();
+        if (should_sync) {
+            runtime.Finish();
+        }
     }
 
     Tegra::Memory::DeviceGuestMemoryScoped<u8, Tegra::Memory::GuestMemoryFlags::UnsafeReadWrite>
@@ -1230,7 +1234,7 @@ void BufferCache<P>::BindHostComputeStorageBuffers() {
         buffer.MarkUsage(offset, size);
 
         if (is_written) {
-            MarkWrittenBuffer(binding.buffer_id, binding.device_addr, size);
+            MarkWrittenBuffer(binding.buffer_id, binding.device_addr, size, true);
         }
 
         if constexpr (NEEDS_BIND_STORAGE_INDEX) {
@@ -1516,10 +1520,12 @@ void BufferCache<P>::UpdateComputeTextureBuffers() {
 }
 
 template <class P>
-void BufferCache<P>::MarkWrittenBuffer(BufferId buffer_id, DAddr device_addr, u32 size) {
+void BufferCache<P>::MarkWrittenBuffer(BufferId buffer_id, DAddr device_addr, u32 size, bool needs_sync) {
     if constexpr (!IS_OPENGL) {
-        Buffer& buffer = slot_buffers[buffer_id];
-        buffer.setWriteTick(runtime.CurrentTick());
+        if (needs_sync) {
+            Buffer& buffer = slot_buffers[buffer_id];
+            buffer.setWriteTick(runtime.CurrentTick());
+        }
     }
     memory_tracker.MarkRegionAsGpuModified(device_addr, size);
     gpu_modified_ranges.Add(device_addr, size);
@@ -1535,8 +1541,11 @@ BufferId BufferCache<P>::FindBuffer(DAddr device_addr, u32 size, bool sparse_com
     const BufferId buffer_id = page_table[page];
     if (buffer_id) {
         Buffer& buffer = slot_buffers[buffer_id];
-        WaitForGpuFenceIfNeeded(buffer);
         if (buffer.IsInBounds(device_addr, size)) {
+            const bool should_sync = Settings::IsGPUFenceBehaviorAccurate();
+            if (should_sync) {
+                SynchronizeBufferWrites(buffer);
+            }
             bool usable = true;
             if constexpr (requires { buffer.IsSparseCompatible(); }) {
                 if (sparse_compatible && !buffer.IsSparseCompatible()) {
@@ -1552,17 +1561,11 @@ BufferId BufferCache<P>::FindBuffer(DAddr device_addr, u32 size, bool sparse_com
 }
 
 template <class P>
-void BufferCache<P>::WaitForGpuFenceIfNeeded(Buffer& buffer) {
+void BufferCache<P>::SynchronizeBufferWrites(Buffer& buffer) {
     if constexpr (!IS_OPENGL) {
-        const bool gpu_fence_accurate = Settings::IsGPUFenceBehaviorAccurate();
-        const bool gpu_fence_strict = Settings::IsGPUFenceBehaviorStrict();
-        if (gpu_fence_accurate || gpu_fence_strict) {
-            const u64 gpu_tick_delay = gpu_fence_strict ? 0 : 3;
-            const u64 buffer_tick = buffer.getWriteTick();
-            const u64 gpu_tick = runtime.KnownGpuTick();
-            if (buffer_tick > gpu_tick + gpu_tick_delay) {
-                runtime.Wait(buffer_tick);
-            }
+        const u64 buffer_tick = buffer.getWriteTick();
+        if (!runtime.IsFree(buffer_tick)) {
+            runtime.Wait(buffer_tick);
         }
     }
 }
@@ -1795,9 +1798,6 @@ void BufferCache<P>::ImmediateUploadMemory([[maybe_unused]] Buffer& buffer,
                 if (immediate_buffer.empty()) {
                     immediate_buffer = ImmediateBuffer(largest_copy);
                 }
-                if (Settings::values.enable_gpu_buffer_readback.GetValue()) {
-                    DownloadBufferMemory(buffer, device_addr, copy.size);
-                }
                 device_memory.ReadBlockUnsafe(device_addr, immediate_buffer.data(), copy.size);
                 upload_span = immediate_buffer.subspan(0, copy.size);
             }
@@ -1816,9 +1816,6 @@ void BufferCache<P>::MappedUploadMemory([[maybe_unused]] Buffer& buffer,
         for (BufferCopy& copy : copies) {
             u8* const src_pointer = staging_pointer.data() + copy.src_offset;
             const DAddr device_addr = buffer.CpuAddr() + copy.dst_offset;
-            if (Settings::values.enable_gpu_buffer_readback.GetValue()) {
-                DownloadBufferMemory(buffer, device_addr, copy.size);
-            }
             device_memory.ReadBlockUnsafe(device_addr, src_pointer, copy.size);
             // Apply the staging offset
             copy.src_offset += upload_staging.offset;
diff --git a/src/video_core/buffer_cache/buffer_cache_base.h b/src/video_core/buffer_cache/buffer_cache_base.h
index 0dbb368c47..26bf3dd9ed 100644
--- a/src/video_core/buffer_cache/buffer_cache_base.h
+++ b/src/video_core/buffer_cache/buffer_cache_base.h
@@ -430,11 +430,11 @@ private:
 
     void UpdateComputeTextureBuffers();
 
-    void MarkWrittenBuffer(BufferId buffer_id, DAddr device_addr, u32 size);
+    void MarkWrittenBuffer(BufferId buffer_id, DAddr device_addr, u32 size, bool needs_sync = false);
 
     [[nodiscard]] BufferId FindBuffer(DAddr device_addr, u32 size, bool sparse_compatible);
 
-    void WaitForGpuFenceIfNeeded(Buffer& buffer);
+    void SynchronizeBufferWrites(Buffer& buffer);
 
     [[nodiscard]] OverlapResult ResolveOverlaps(DAddr device_addr, u32 wanted_size);