[video_core] Reduce synchronization overhead and improve performance in DMA operations (#3179)

This reworks the logic to improve performance in many games that heavily rely on DMA. It can help all platforms, but on desktop the performance boost can be noticeable, especially on dedicated GPUs. The option Sync Memory Operations must be enabled.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3179
Co-authored-by: MaranBr <maranbr@outlook.com>
Co-committed-by: MaranBr <maranbr@outlook.com>

src/video_core/dma_pusher.cpp

@@ -43,80 +43,56 @@ void DmaPusher::DispatchCalls() {
 
 bool DmaPusher::Step() {
     if (!ib_enable || dma_pushbuffer.empty()) {
-        // pushbuffer empty and IB empty or nonexistent - nothing to do
         return false;
     }
 
-    CommandList& command_list{dma_pushbuffer.front()};
+    CommandList& command_list = dma_pushbuffer.front();
 
-    ASSERT_OR_EXECUTE(
-        command_list.command_lists.size() || command_list.prefetch_command_list.size(), {
-            // Somehow the command_list is empty, in order to avoid a crash
-            // We ignore it and assume its size is 0.
+    const size_t prefetch_size = command_list.prefetch_command_list.size();
+    const size_t command_list_size = command_list.command_lists.size();
+
+    if (prefetch_size == 0 && command_list_size == 0) {
         dma_pushbuffer.pop();
         dma_pushbuffer_subindex = 0;
         return true;
-        });
+    }
 
-    if (command_list.prefetch_command_list.size()) {
-        // Prefetched command list from nvdrv, used for things like synchronization
-        ProcessCommands(VideoCommon::FixSmallVectorADL(command_list.prefetch_command_list));
+    if (prefetch_size > 0) {
+        ProcessCommands(command_list.prefetch_command_list);
         dma_pushbuffer.pop();
-    } else {
-        const CommandListHeader command_list_header{
-            command_list.command_lists[dma_pushbuffer_subindex++]};
+        return true;
+    }
 
-        if (signal_sync) {
+    auto& current_command = command_list.command_lists[dma_pushbuffer_subindex];
+    const CommandListHeader& header = current_command;
+    dma_state.dma_get = header.addr;
+
+    if (signal_sync && !synced) {
         std::unique_lock lk(sync_mutex);
         sync_cv.wait(lk, [this]() { return synced; });
         signal_sync = false;
         synced = false;
     }
 
-        dma_state.dma_get = command_list_header.addr;
-
-        if (command_list_header.size == 0) {
-            return true;
-        }
-
-        // Push buffer non-empty, read a word
-        if (dma_state.method >= MacroRegistersStart) {
-            if (subchannels[dma_state.subchannel]) {
-                subchannels[dma_state.subchannel]->current_dirty = memory_manager.IsMemoryDirty(
-                    dma_state.dma_get, command_list_header.size * sizeof(u32));
-            }
+    if (header.size > 0 && dma_state.method >= MacroRegistersStart && subchannels[dma_state.subchannel]) {
+        subchannels[dma_state.subchannel]->current_dirty = memory_manager.IsMemoryDirty(dma_state.dma_get, header.size * sizeof(u32));
     }
 
-        const auto safe_process = [&] {
-            Tegra::Memory::GpuGuestMemory<Tegra::CommandHeader,
-                                          Tegra::Memory::GuestMemoryFlags::SafeRead>
-                headers(memory_manager, dma_state.dma_get, command_list_header.size,
-                        &command_headers);
-            ProcessCommands(headers);
-        };
-
-        const auto unsafe_process = [&] {
-            Tegra::Memory::GpuGuestMemory<Tegra::CommandHeader,
-                                          Tegra::Memory::GuestMemoryFlags::UnsafeRead>
-                headers(memory_manager, dma_state.dma_get, command_list_header.size,
-                        &command_headers);
+    if (header.size > 0) {
+        if (Settings::IsDMALevelDefault() ? (Settings::IsGPULevelMedium() || Settings::IsGPULevelHigh()) : Settings::IsDMALevelSafe()) {
+            Tegra::Memory::GpuGuestMemory<Tegra::CommandHeader, Tegra::Memory::GuestMemoryFlags::SafeRead>headers(memory_manager, dma_state.dma_get, header.size, &command_headers);
             ProcessCommands(headers);
-        };
-
-        const bool use_safe = Settings::IsDMALevelDefault() ? (Settings::IsGPULevelMedium() || Settings::IsGPULevelHigh()) : Settings::IsDMALevelSafe();
-
-        if (use_safe) {
-            safe_process();
         } else {
-            unsafe_process();
+            Tegra::Memory::GpuGuestMemory<Tegra::CommandHeader, Tegra::Memory::GuestMemoryFlags::UnsafeRead>headers(memory_manager, dma_state.dma_get, header.size, &command_headers);
+            ProcessCommands(headers);
+        }
     }
 
-        if (dma_pushbuffer_subindex >= command_list.command_lists.size()) {
-            // We've gone through the current list, remove it from the queue
+    if (++dma_pushbuffer_subindex >= command_list_size) {
         dma_pushbuffer.pop();
         dma_pushbuffer_subindex = 0;
-        } else if (command_list.command_lists[dma_pushbuffer_subindex].sync && Settings::values.sync_memory_operations.GetValue()) {
-            signal_sync = true;
+    } else {
+        signal_sync = command_list.command_lists[dma_pushbuffer_subindex].sync && Settings::values.sync_memory_operations.GetValue();
     }
 
     if (signal_sync) {
@@ -126,7 +102,7 @@ bool DmaPusher::Step() {
             sync_cv.notify_all();
         });
     }
-    }
+
     return true;
 }