Revert "[dxvk] Remove dxvk.lowLatencyAllowCpuFramesOverlap config variable"

This reverts commit c802bdf42e and makes small adjustments.
Until we have a proper synchronization in place between emitting Cs triggered by the app thread, and fetching them from the queue, to measure the CsThread-caused delay, this config option is still useful for running some rare CsThread-limited games.

src/dxvk/dxvk_options.cpp

@@ -20,6 +20,8 @@ namespace dxvk {
     allowFse              = config.getOption<bool>    ("dxvk.allowFse",               false);
     framePace             = config.getOption<std::string>("dxvk.framePace",           "");
     lowLatencyOffset      = config.getOption<int32_t> ("dxvk.lowLatencyOffset",       0);
+    lowLatencyAllowCpuFramesOverlap
+                          = config.getOption<bool>    ("dxvk.lowLatencyAllowCpuFramesOverlap", true);
     deviceFilter          = config.getOption<std::string>("dxvk.deviceFilter",        "");
     tilerMode             = config.getOption<Tristate>("dxvk.tilerMode",              Tristate::Auto);
   }

src/dxvk/framepacer/dxvk_framepacer.cpp

@@ -71,6 +71,7 @@ namespace dxvk {
 
     m_mode->signalGpuStart       ( firstFrameId-1 );
     m_mode->signalRenderFinished ( firstFrameId-1 );
+    m_mode->signalCsFinished     ( firstFrameId );
   }
 
 

src/dxvk/framepacer/dxvk_framepacer.h

@@ -53,6 +53,7 @@ namespace dxvk {
       auto now = high_resolution_clock::now();
       LatencyMarkers* m = m_latencyMarkersStorage.getMarkers(frameId);
       m->csFinished = std::chrono::duration_cast<microseconds>(now - m->start).count();
+      m_mode->signalCsFinished( frameId );
     }
 
     void notifySubmit( uint64_t frameId ) override {

src/dxvk/framepacer/dxvk_framepacer_mode.h

@@ -44,6 +44,9 @@ namespace dxvk {
     void signalGpuStart( uint64_t frameId ) {
       if (m_mode) m_fenceGpuStart.signal(frameId); }
 
+    void signalCsFinished( uint64_t frameId ) {
+      if (m_mode) m_fenceCsFinished.signal(frameId); }
+
     void setTargetFrameRate( double frameRate ) {
       if (!m_fpsLimitEnvOverride && frameRate > 1.0)
         m_fpsLimitFrametime.store( 1'000'000/frameRate );
@@ -65,6 +68,7 @@ namespace dxvk {
 
     sync::Fence m_fenceGpuStart    = { sync::Fence(DXGI_MAX_SWAP_CHAIN_BUFFERS) };
     sync::Fence m_fenceGpuFinished = { sync::Fence(DXGI_MAX_SWAP_CHAIN_BUFFERS) };
+    sync::Fence m_fenceCsFinished  = { sync::Fence(DXGI_MAX_SWAP_CHAIN_BUFFERS) };
 
   };
 

src/dxvk/framepacer/dxvk_framepacer_mode_low_latency.cpp

@@ -10,6 +10,15 @@ namespace dxvk {
   }
 
 
+  bool getLowLatencyAllowCpuFramesOverlapFromEnv( bool& allowOverlap ) {
+    int32_t o;
+    if (!FramePacerMode::getIntFromEnv("DXVK_LOW_LATENCY_ALLOW_CPU_FRAMES_OVERLAP", &o))
+      return false;
+    allowOverlap = (bool) o;
+    return true;
+  }
+
+
   int32_t LowLatencyMode::getLowLatencyOffset( const DxvkOptions& options ) {
     int32_t offset = options.lowLatencyOffset;
     int32_t o;
@@ -21,4 +30,14 @@ namespace dxvk {
     return offset;
   }
 
+
+  bool LowLatencyMode::getLowLatencyAllowCpuFramesOverlap( const DxvkOptions& options ) {
+    bool allowOverlap = options.lowLatencyAllowCpuFramesOverlap;
+    bool o;
+    if (getLowLatencyAllowCpuFramesOverlapFromEnv(o))
+      allowOverlap = o;
+    return allowOverlap;
+  }
+
+
 }

src/dxvk/framepacer/dxvk_framepacer_mode_low_latency.h

@@ -44,17 +44,21 @@ namespace dxvk {
 
     LowLatencyMode(Mode mode, LatencyMarkersStorage* storage, const DxvkOptions& options)
     : FramePacerMode(mode, storage),
-      m_lowLatencyOffset(getLowLatencyOffset(options)) {
+      m_lowLatencyOffset(getLowLatencyOffset(options)),
+      m_allowCpuFramesOverlap(getLowLatencyAllowCpuFramesOverlap(options)) {
       Logger::info( str::format("Using lowLatencyOffset: ", m_lowLatencyOffset) );
+      Logger::info( str::format("Using lowLatencyAllowCpuFramesOverlap: ", m_allowCpuFramesOverlap) );
     }
 
     ~LowLatencyMode() {}
 
 
     void startFrame( uint64_t frameId ) override {
-
       using std::chrono::duration_cast;
 
+      if (!m_allowCpuFramesOverlap)
+        m_fenceCsFinished.wait( frameId-1 );
+
       m_fenceGpuStart.wait( frameId-1 );
 
       time_point now = high_resolution_clock::now();
@@ -227,7 +231,10 @@ namespace dxvk {
 
 
     int32_t getLowLatencyOffset( const DxvkOptions& options );
+    bool getLowLatencyAllowCpuFramesOverlap( const DxvkOptions& options );
+
     const int32_t m_lowLatencyOffset;
+    const bool    m_allowCpuFramesOverlap;
 
     Sleep::TimePoint m_lastStart = { high_resolution_clock::now() };
     std::array<SyncProps, 16> m_props;