Fine-tuning of frame pacing logic

src/video_core/renderer_vulkan/vk_scheduler.h

@@ -16,8 +16,8 @@
 
 #include "common/alignment.h"
 #include "common/common_types.h"
-#include "common/settings.h"
 #include "common/polyfill_thread.h"
+#include "common/settings.h"
 #include "video_core/renderer_vulkan/vk_master_semaphore.h"
 #include "video_core/vulkan_common/vulkan_wrapper.h"
 
@@ -114,29 +114,40 @@ public:
 
     /// Waits for the given GPU tick, optionally pacing frames.
     void Wait(u64 tick, double target_fps = 0.0) {
+        if (tick > 0) {
+            if (tick >= master_semaphore->CurrentTick()) {
+                Flush();
+            }
+            master_semaphore->Wait(tick);
+        }
         if (Settings::values.use_speed_limit.GetValue() && target_fps > 0.0) {
-            const auto now = std::chrono::steady_clock::now();
-            if (start_time == std::chrono::steady_clock::time_point{} || current_target_fps != target_fps) {
-                start_time = now;
+            auto now = std::chrono::steady_clock::now();
+            if (last_target_fps != target_fps) {
+                max_frame_count = static_cast<int>(0.1 * target_fps);
+                frame_interval = std::chrono::duration_cast<std::chrono::steady_clock::duration>(std::chrono::duration<double>(1.0 / target_fps));
+                last_target_fps = target_fps;
                 frame_counter = 0;
-                current_target_fps = target_fps;
+                start_time = now;
             }
             frame_counter++;
-            std::chrono::duration<double> frame_interval(1.0 / current_target_fps);
             auto target_time = start_time + frame_interval * frame_counter;
-            if (target_time > now) {
-                std::this_thread::sleep_until(target_time);
-            } else {
-                start_time = now;
+            if (target_time >= now) {
+                auto sleep_time = target_time - now;
+                if (sleep_time > std::chrono::milliseconds(15)) {
+                    std::this_thread::sleep_for(sleep_time - std::chrono::milliseconds(1));
+                }
+                while (std::chrono::steady_clock::now() < target_time) {
+#ifdef _WIN32
+                    _mm_pause();
+#else
+                    std::this_thread::yield();
+#endif
+                }
+            } else if (frame_counter > max_frame_count) {
                 frame_counter = 0;
+                start_time = now;
             }
         }
-        if (tick > 0) {
-            if (tick >= master_semaphore->CurrentTick()) {
-                Flush();
-            }
-            master_semaphore->Wait(tick);
-        }
     }
 
     /// Returns the master timeline semaphore.
@@ -281,9 +292,11 @@ private:
     std::condition_variable_any event_cv;
     std::jthread worker_thread;
 
+    std::chrono::steady_clock::time_point frame_interval{};
     std::chrono::steady_clock::time_point start_time{};
+    double last_target_fps{};
+    u64 max_frame_count{};
     u64 frame_counter{};
-    double current_target_fps{};
 };
 
 } // namespace Vulkan