More Steam Link performance optimizations

app/deploy/steamlink/moonlight.sh

@@ -5,5 +5,9 @@
 # pairing data will be lost each reboot.
 HOME=/usr/local/moonlight
 
+# Renice PE_Single_CPU which seems to host A/V stuff
+renice -10 -p $(pidof PE_Single_CPU)
+
+# Renice Moonlight itself to avoid preemption by background tasks
 # Write output to a logfile in /tmp
-exec ./bin/moonlight > /tmp/moonlight.log
+exec nice -n -10 ./bin/moonlight > /tmp/moonlight.log

app/streaming/audio/audio.cpp

@@ -111,8 +111,11 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
 {
     int samplesDecoded;
 
-    // Set this thread to high priority to reduce
-    // the chance of missing our sample delivery time
+#ifndef STEAM_LINK
+    // Set this thread to high priority to reduce the chance of missing
+    // our sample delivery time. On Steam Link, this causes starvation
+    // of other threads due to severely restricted CPU time available,
+    // so we will skip it on that platform.
     if (s_ActiveSession->m_AudioSampleCount == 0) {
         if (SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH) < 0) {
             SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
@@ -120,6 +123,7 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
                         SDL_GetError());
         }
     }
+#endif
 
     // See if we need to drop this sample
     if (s_ActiveSession->m_DropAudioEndTime != 0) {

app/streaming/session.cpp

@@ -49,7 +49,12 @@ AUDIO_RENDERER_CALLBACKS Session::k_AudioCallbacks = {
     nullptr,
     Session::arCleanup,
     Session::arDecodeAndPlaySample,
-    CAPABILITY_DIRECT_SUBMIT
+    CAPABILITY_DIRECT_SUBMIT |
+#ifdef STEAM_LINK
+    CAPABILITY_SLOW_OPUS_DECODER
+#else
+    0
+#endif
 };
 
 Session* Session::s_ActiveSession;