[idd] elect the fastest frame timing client

idd/LGIdd/CFrameScheduler.cpp

@@ -0,0 +1,216 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "CFrameScheduler.h"
+
+#include "CDebug.h"
+
+static const uint64_t MIN_PERIOD_NS = 2000000ULL;
+static const uint64_t MAX_PERIOD_NS = 1000000000ULL;
+static const uint32_t MIN_LEASE_MS  = 100;
+static const uint32_t MAX_LEASE_MS  = 5000;
+
+uint64_t CFrameScheduler::Nanotime()
+{
+  static const uint64_t frequency = []()
+  {
+    LARGE_INTEGER value;
+    QueryPerformanceFrequency(&value);
+    return static_cast<uint64_t>(value.QuadPart);
+  }();
+
+  LARGE_INTEGER counter;
+  QueryPerformanceCounter(&counter);
+  const uint64_t ticks = static_cast<uint64_t>(counter.QuadPart);
+  return ticks / frequency * 1000000000ULL +
+    ticks % frequency * 1000000000ULL / frequency;
+}
+
+CFrameScheduler::Client * CFrameScheduler::FindClient(uint32_t clientID)
+{
+  if (!clientID)
+    return nullptr;
+
+  for (Client& client : m_clients)
+    if (client.clientID == clientID)
+      return &client;
+
+  return nullptr;
+}
+
+void CFrameScheduler::ElectOwner(uint64_t now)
+{
+  Client * fastest     = nullptr;
+  Client * incumbent   = FindClient(m_schedule.clientID);
+  unsigned subscribers = 0;
+
+  for (Client& client : m_clients)
+  {
+    if (!client.subscribed)
+      continue;
+
+    ++subscribers;
+    if (!client.active || client.expiry <= now)
+    {
+      client.active = false;
+      fastest       = nullptr;
+      break;
+    }
+
+    if (!fastest || client.period < fastest->period)
+      fastest = &client;
+  }
+
+  if (!subscribers)
+    fastest = nullptr;
+
+  if (fastest && incumbent && incumbent->subscribed && incumbent->active &&
+      incumbent->expiry > now &&
+      incumbent->period <= fastest->period + fastest->period / 200)
+    fastest = incumbent;
+
+  const uint32_t oldClientID   = m_schedule.clientID;
+  const uint32_t oldGeneration = m_schedule.generation;
+  if (!fastest)
+  {
+    m_schedule   = {};
+    m_scheduling = false;
+  }
+  else
+  {
+    m_schedule.clientID    = fastest->clientID;
+    m_schedule.generation  = fastest->generation;
+    m_schedule.period      = fastest->period;
+    m_schedule.targetSlack = fastest->targetSlack;
+    m_scheduling = true;
+  }
+
+  if (oldClientID != m_schedule.clientID ||
+      oldGeneration != m_schedule.generation)
+  {
+    if (m_scheduling)
+      DEBUG_INFO("Frame timing owner %u generation %u at %.3f Hz",
+        m_schedule.clientID, m_schedule.generation,
+        1000000000.0 / m_schedule.period);
+    else if (oldClientID)
+      DEBUG_INFO("Frame timing owner released; using push delivery");
+  }
+}
+
+void CFrameScheduler::Reset()
+{
+  AcquireSRWLockExclusive(&m_lock);
+  for (Client& client : m_clients)
+    client = {};
+  m_schedule   = {};
+  m_scheduling = false;
+  ReleaseSRWLockExclusive(&m_lock);
+}
+
+void CFrameScheduler::UpdateSubscribers(const uint32_t * clientIDs,
+  unsigned count, uint64_t now)
+{
+  AcquireSRWLockExclusive(&m_lock);
+
+  for (Client& client : m_clients)
+    client.subscribed = false;
+
+  for (unsigned i = 0; i < count; ++i)
+  {
+    Client * client = FindClient(clientIDs[i]);
+    if (!client)
+      for (Client& candidate : m_clients)
+        if (!candidate.clientID)
+        {
+          candidate.clientID = clientIDs[i];
+          client = &candidate;
+          break;
+        }
+
+    if (client)
+      client->subscribed = true;
+  }
+
+  for (Client& client : m_clients)
+    if (client.clientID && !client.subscribed)
+      client = {};
+
+  ElectOwner(now);
+  ReleaseSRWLockExclusive(&m_lock);
+}
+
+bool CFrameScheduler::UpdateSchedule(const KVMFRFrameSchedule& schedule,
+  uint64_t now)
+{
+  static const KVMFRFrameScheduleFlags validFlags =
+    KVMFR_FRAME_SCHEDULE_ACTIVE    |
+    KVMFR_FRAME_SCHEDULE_RELEASE   |
+    KVMFR_FRAME_SCHEDULE_RESET     |
+    KVMFR_FRAME_SCHEDULE_IMMEDIATE;
+
+  if (!schedule.clientID || schedule.flags & ~validFlags)
+    return false;
+
+  AcquireSRWLockExclusive(&m_lock);
+  Client * client = FindClient(schedule.clientID);
+  if (!client || !client->subscribed)
+  {
+    ReleaseSRWLockExclusive(&m_lock);
+    return false;
+  }
+
+  if (schedule.flags & KVMFR_FRAME_SCHEDULE_RELEASE)
+  {
+    client->active = false;
+    client->expiry = 0;
+    ElectOwner(now);
+    ReleaseSRWLockExclusive(&m_lock);
+    return true;
+  }
+
+  if (!(schedule.flags & KVMFR_FRAME_SCHEDULE_ACTIVE) ||
+      schedule.period < MIN_PERIOD_NS ||
+      schedule.period > MAX_PERIOD_NS ||
+      schedule.targetSlack >= schedule.period ||
+      schedule.lease < MIN_LEASE_MS || schedule.lease > MAX_LEASE_MS)
+  {
+    ReleaseSRWLockExclusive(&m_lock);
+    return false;
+  }
+
+  client->generation  = schedule.generation;
+  client->period      = schedule.period;
+  client->targetSlack = schedule.targetSlack;
+  client->expiry      = now + static_cast<uint64_t>(schedule.lease) * 1000000;
+  client->active      = true;
+  ElectOwner(now);
+  ReleaseSRWLockExclusive(&m_lock);
+  return true;
+}
+
+bool CFrameScheduler::GetSchedule(Schedule& schedule) const
+{
+  AcquireSRWLockShared(&m_lock);
+  const bool result = m_scheduling;
+  if (result)
+    schedule = m_schedule;
+  ReleaseSRWLockShared(&m_lock);
+  return result;
+}