[client] display: use trusted nominal cadence

Always track Wayland surface outputs alongside fractional scaling and use
RandR modes for X11 cadence. Remove render-derived feedback so a
throttled client cannot teach the producer to remain throttled.

Release scheduling after nominal output timing remains unavailable.

client/displayservers/Wayland/presentation.c

@@ -76,15 +76,7 @@ bool waylandGetFramePeriod(uint64_t * period)
   /* Frame demand must use the output's nominal rate. Basing demand on the
    * observed presentation interval can lock a VRR session at its current,
    * slower cadence. */
-  if (waylandOutputGetFramePeriod(period))
-    return true;
-
-  const uint64_t value = atomic_load(&wlWm.presentationPeriod);
-  if (!value)
-    return false;
-
-  *period = value;
-  return true;
+  return waylandOutputGetFramePeriod(period);
 }
 
 static void presentationFeedbackDiscarded(void * data,

client/displayservers/Wayland/window.c

@@ -133,6 +133,8 @@ bool waylandWindowInit(const char * title, const char * appId, bool fullscreen,
     return false;
   }
 
+  wl_surface_add_listener(wlWm.surface, &wlSurfaceListener, NULL);
+
   if (wlWm.fractionalScaleManager)
   {
     wlWm.fractionalScaleInterface = wp_fractional_scale_manager_v1_get_fractional_scale(
@@ -140,8 +142,6 @@ bool waylandWindowInit(const char * title, const char * appId, bool fullscreen,
     wp_fractional_scale_v1_add_listener(wlWm.fractionalScaleInterface,
         &fractionalScaleListener, NULL);
   }
-  else
-    wl_surface_add_listener(wlWm.surface, &wlSurfaceListener, NULL);
 
   if (wlWm.contentTypeManager)
   {

client/displayservers/X11/CMakeLists.txt

@@ -10,6 +10,7 @@ pkg_check_modules(DISPLAYSERVER_X11 REQUIRED IMPORTED_TARGET
   xinerama
   xcursor
   xpresent
+  xrandr
   xkbcommon
 )
 

client/displayservers/X11/x11.c

@@ -38,6 +38,7 @@
 #include <X11/extensions/scrnsaver.h>
 #include <X11/extensions/Xinerama.h>
 #include <X11/extensions/Xpresent.h>
+#include <X11/extensions/Xrandr.h>
 #include <X11/Xcursor/Xcursor.h>
 #include <X11/XKBlib.h>
 
@@ -94,6 +95,67 @@ static void x11XPresentEvent(XGenericEventCookie *cookie);
 static void x11UpdateKeyboardGroup(void);
 static void x11GrabPointer(void);
 
+static uint64_t x11ModePeriod(
+    const XRRScreenResources * resources, RRMode modeID)
+{
+  for (int i = 0; i < resources->nmode; ++i)
+  {
+    const XRRModeInfo * mode = resources->modes + i;
+    if (mode->id != modeID || !mode->dotClock ||
+        !mode->hTotal || !mode->vTotal)
+      continue;
+
+    uint64_t pixels = (uint64_t)mode->hTotal * mode->vTotal;
+    if (mode->modeFlags & RR_DoubleScan)
+      pixels *= 2;
+    if (mode->modeFlags & RR_Interlace)
+      pixels /= 2;
+
+    return pixels / mode->dotClock * 1000000000ULL +
+      pixels % mode->dotClock * 1000000000ULL / mode->dotClock;
+  }
+
+  return 0;
+}
+
+static void x11UpdateFramePeriod(void)
+{
+  uint64_t fastest = 0;
+  const Window root = DefaultRootWindow(x11.display);
+  XRRScreenResources * resources =
+    XRRGetScreenResourcesCurrent(x11.display, root);
+  if (!resources)
+  {
+    atomic_store(&x11.nominalPeriod, 0);
+    return;
+  }
+
+  for (int i = 0; i < resources->ncrtc; ++i)
+  {
+    XRRCrtcInfo * crtc =
+      XRRGetCrtcInfo(x11.display, resources, resources->crtcs[i]);
+    if (!crtc)
+      continue;
+
+    const bool intersects = crtc->mode && crtc->width && crtc->height &&
+      x11.rect.x < crtc->x + (int)crtc->width &&
+      x11.rect.x + x11.rect.w > crtc->x &&
+      x11.rect.y < crtc->y + (int)crtc->height &&
+      x11.rect.y + x11.rect.h > crtc->y;
+    if (intersects)
+    {
+      const uint64_t candidate = x11ModePeriod(resources, crtc->mode);
+      if (candidate && (!fastest || candidate < fastest))
+        fastest = candidate;
+    }
+
+    XRRFreeCrtcInfo(crtc);
+  }
+
+  XRRFreeScreenResources(resources);
+  atomic_store(&x11.nominalPeriod, fastest);
+}
+
 static void x11DoPresent(uint64_t msc)
 {
   static bool startup = true;
@@ -284,6 +346,12 @@ static bool x11Init(const LG_DSInitParams params)
   x11.display   = XOpenDisplay(NULL);
   x11.jitRender = params.jitRender;
   x11.wm        = &X11WM_Default;
+  x11.rect      = (struct Rect) {
+    .x = params.x,
+    .y = params.y,
+    .w = params.w,
+    .h = params.h,
+  };
 
   XSetWindowAttributes swa =
   {
@@ -689,6 +757,18 @@ static bool x11Init(const LG_DSInitParams params)
   /* default to the square cursor */
   XDefineCursor(x11.display, x11.window, x11.cursors[LG_POINTER_SQUARE]);
 
+  x11.xrandrSupported =
+    XRRQueryExtension(x11.display, &x11.xrandrEvent, &error);
+  if (x11.xrandrSupported)
+  {
+    XRRSelectInput(x11.display, DefaultRootWindow(x11.display),
+      RRScreenChangeNotifyMask | RRCrtcChangeNotifyMask |
+      RROutputChangeNotifyMask);
+    x11UpdateFramePeriod();
+  }
+  else
+    DEBUG_WARN("X11 nominal output refresh is unavailable");
+
   if (x11.jitRender)
   {
     x11.frameEvent = lgCreateEvent(true, 0);
@@ -899,6 +979,16 @@ static int x11EventThread(void * unused)
     XEvent xe;
     XNextEvent(x11.display, &xe);
 
+    if (x11.xrandrSupported &&
+        (xe.type == x11.xrandrEvent + RRScreenChangeNotify ||
+         xe.type == x11.xrandrEvent + RRNotify))
+    {
+      if (xe.type == x11.xrandrEvent + RRScreenChangeNotify)
+        XRRUpdateConfiguration(&xe);
+      x11UpdateFramePeriod();
+      continue;
+    }
+
     // call the clipboard handling code
     if (x11CBEventThread(&xe))
       continue;
@@ -932,6 +1022,8 @@ static int x11EventThread(void * unused)
         x11.rect.y = y;
         x11.rect.w = xe.xconfigure.width;
         x11.rect.h = xe.xconfigure.height;
+        if (x11.xrandrSupported)
+          x11UpdateFramePeriod();
 
         app_updateWindowPos(x, y);
 
@@ -1507,7 +1599,7 @@ static void x11XPresentEvent(XGenericEventCookie *cookie)
 
 static bool x11GetFramePeriod(uint64_t * period)
 {
-  const uint64_t value = atomic_load(&x11.presentPeriod);
+  const uint64_t value = atomic_load(&x11.nominalPeriod);
   if (!value)
     return false;
 

client/displayservers/X11/x11.h

@@ -76,11 +76,15 @@ struct X11DSState
   bool              jitRender;
   _Atomic(uint64_t) presentMsc, presentUst;
   _Atomic(uint64_t) presentPeriod;
+  _Atomic(uint64_t) nominalPeriod;
   uint32_t          presentSerial;
   Pixmap            presentPixmap;
   XserverRegion     presentRegion;
   LGEvent *         frameEvent;
 
+  bool xrandrSupported;
+  int  xrandrEvent;
+
   LGThread * eventThread;
 
   int xinputOp;

client/src/frame_scheduler.c

@@ -26,16 +26,15 @@
 #include "common/time.h"
 
 #include <stdbool.h>
-#include <stdlib.h>
 #include <string.h>
 
-#define FRAME_SCHEDULER_LEASE_MS        1000U
-#define FRAME_SCHEDULER_RENEW_NS        250000000ULL
-#define FRAME_SCHEDULER_FEEDBACK_NS     50000000ULL
-#define FRAME_SCHEDULER_TARGET_SLACK_NS 500000ULL
-#define FRAME_SCHEDULER_MIN_PERIOD_NS   2000000ULL
-#define FRAME_SCHEDULER_MAX_PERIOD_NS   1000000000ULL
-#define FRAME_SCHEDULER_SAMPLE_COUNT    9U
+#define FRAME_SCHEDULER_LEASE_MS          1000U
+#define FRAME_SCHEDULER_RENEW_NS          250000000ULL
+#define FRAME_SCHEDULER_FEEDBACK_NS       50000000ULL
+#define FRAME_SCHEDULER_CADENCE_GRACE_NS 500000000ULL
+#define FRAME_SCHEDULER_TARGET_SLACK_NS   500000ULL
+#define FRAME_SCHEDULER_MIN_PERIOD_NS     2000000ULL
+#define FRAME_SCHEDULER_MAX_PERIOD_NS     1000000000ULL
 
 static struct
 {
@@ -47,6 +46,7 @@ static struct
   _Atomic(uint32_t) generation;
   _Atomic(uint64_t) period;
   uint64_t          lastSend;
+  uint64_t          lastCadence;
 
   int64_t  phaseError;
   uint32_t feedbackFrameSerial;
@@ -54,43 +54,9 @@ static struct
   bool     feedbackDirty;
 
   LG_TransportControlToken controlToken;
-
-  uint64_t renderSamples[FRAME_SCHEDULER_SAMPLE_COUNT];
-  unsigned renderSampleIndex;
-  unsigned renderSampleCount;
-  uint64_t lastRender;
 }
 l_frameScheduler;
 
-static int compareU64(const void * a, const void * b)
-{
-  const uint64_t lhs = *(const uint64_t *)a;
-  const uint64_t rhs = *(const uint64_t *)b;
-  return (lhs > rhs) - (lhs < rhs);
-}
-
-static uint64_t fallbackPeriod(void)
-{
-  uint64_t samples[FRAME_SCHEDULER_SAMPLE_COUNT];
-  unsigned count;
-
-  LG_LOCK(l_frameScheduler.lock);
-  count = l_frameScheduler.renderSampleCount;
-  memcpy(samples, l_frameScheduler.renderSamples,
-      count * sizeof(*samples));
-  LG_UNLOCK(l_frameScheduler.lock);
-
-  if (count < 5)
-    return 0;
-
-  qsort(samples, count, sizeof(*samples), compareU64);
-  const uint64_t period = samples[count / 2];
-  if (samples[count * 3 / 4] - samples[count / 4] > period / 20)
-    return 0;
-
-  return period;
-}
-
 static uint64_t presentationPeriod(void)
 {
   uint64_t period = 0;
@@ -98,7 +64,7 @@ static uint64_t presentationPeriod(void)
       g_state.ds->getFramePeriod(&period))
     return period;
 
-  return fallbackPeriod();
+  return 0;
 }
 
 static bool controlReady(void)
@@ -177,6 +143,7 @@ void frameScheduler_start(LG_TransportFeatureFlags features)
   l_frameScheduler.active         = false;
   l_frameScheduler.controlPending = false;
   l_frameScheduler.lastSend       = 0;
+  l_frameScheduler.lastCadence    = 0;
   ++l_frameScheduler.generation;
 
   LG_LOCK(l_frameScheduler.lock);
@@ -203,15 +170,27 @@ void frameScheduler_update(void)
     return;
 
   const uint64_t now = nanotime();
-  uint64_t period    = presentationPeriod();
+  const uint64_t period = presentationPeriod();
   if (period < FRAME_SCHEDULER_MIN_PERIOD_NS ||
       period > FRAME_SCHEDULER_MAX_PERIOD_NS)
   {
-    period = l_frameScheduler.period;
-    if (period < FRAME_SCHEDULER_MIN_PERIOD_NS ||
-        period > FRAME_SCHEDULER_MAX_PERIOD_NS)
-      return;
+    if (l_frameScheduler.active && l_frameScheduler.lastCadence &&
+        now - l_frameScheduler.lastCadence >
+          FRAME_SCHEDULER_CADENCE_GRACE_NS &&
+        sendSchedule(LG_TRANSPORT_FRAME_SCHEDULE_RELEASE, 0))
+    {
+      l_frameScheduler.active = false;
+      l_frameScheduler.period = 0;
+      LG_LOCK(l_frameScheduler.lock);
+      l_frameScheduler.phaseError          = 0;
+      l_frameScheduler.feedbackFrameSerial = 0;
+      l_frameScheduler.feedbackSamples     = 0;
+      l_frameScheduler.feedbackDirty       = false;
+      LG_UNLOCK(l_frameScheduler.lock);
+    }
+    return;
   }
+  l_frameScheduler.lastCadence = now;
 
   bool reset = !l_frameScheduler.period;
   if (!reset)
@@ -259,24 +238,6 @@ void frameScheduler_update(void)
   }
 }
 
-void frameScheduler_observeRender(uint64_t timestamp)
-{
-  LG_LOCK(l_frameScheduler.lock);
-  if (l_frameScheduler.lastRender &&
-      timestamp > l_frameScheduler.lastRender)
-  {
-    l_frameScheduler.renderSamples[l_frameScheduler.renderSampleIndex] =
-      timestamp - l_frameScheduler.lastRender;
-    l_frameScheduler.renderSampleIndex =
-      (l_frameScheduler.renderSampleIndex + 1) %
-        FRAME_SCHEDULER_SAMPLE_COUNT;
-    if (l_frameScheduler.renderSampleCount < FRAME_SCHEDULER_SAMPLE_COUNT)
-      ++l_frameScheduler.renderSampleCount;
-  }
-  l_frameScheduler.lastRender = timestamp;
-  LG_UNLOCK(l_frameScheduler.lock);
-}
-
 void frameScheduler_feedback(uint64_t frameSerial, uint32_t generation,
     uint64_t measuredPhase)
 {

client/src/frame_scheduler.h

@@ -30,7 +30,6 @@ void frameScheduler_free(void);
 void frameScheduler_start(LG_TransportFeatureFlags features);
 void frameScheduler_stop(void);
 void frameScheduler_update(void);
-void frameScheduler_observeRender(uint64_t timestamp);
 void frameScheduler_feedback(uint64_t frameSerial, uint32_t generation,
     uint64_t measuredPhase);
 

client/src/main.c

@@ -727,7 +727,6 @@ static int renderThread(void * unused)
     const uint64_t delta = t - g_state.lastRenderTime;
 
     g_state.lastRenderTime = t;
-    frameScheduler_observeRender(t);
     atomic_fetch_add_explicit(&g_state.renderCount, 1, memory_order_relaxed);
 
     if (!g_state.jitRender && g_params.fpsMin != 0)