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feat: Adds dynamic thread idle to address CPU usage (#2370)

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## Summary
- **Timer-aware idle sleep**: Exposes `Timer.MillisecondsUntilNextTick()` to calculate remaining ms until the next timer wheel tick (0–8ms). The game loop sleeps for that duration minus a 1ms safety margin, instead of spinning at 100% CPU.
- **I/O completion wakeup**: Replaces `Thread.Sleep` with `NetState.WaitForCompletion()`, which uses platform-native completion notification (RIO `RIONotify` on Windows, `eventfd` on Linux, `kevent` timeout on macOS) to wake immediately when network data arrives during sleep.
- **Always-on**: Removes the debug-only `core.enableIdleCPU` config gate. The sleep is self-regulating — under load, `MillisecondsUntilNextTick` returns 0 so no sleep occurs (zero overhead). On idle, CPU drops from ~100% to ~1%.
- **CPS calculation cleanup**: Replaces the 128-element ring buffer with an EMA (exponential moving average) for `CyclesPerSecond`/`AverageCPS` — fewer allocations, no LINQ `.Average()` call each sample.
- **IORingGroup 1.0.6**: Adds `WaitForCompletion(int timeoutMs)` to the `IIORingGroup` interface with platform implementations:
  - **Windows**: `RIONotify` arms the CQ event, `WaitForSingleObject` with timeout
  - **Linux**: `eventfd` registered with io_uring, `poll()` with timeout
  - **macOS**: `kevent()` with timeout

## Test plan
- [ ] Build succeeds on all platforms (`dotnet build`)
- [ ] Empty server: verify CPU usage drops from ~100% to ~1% idle
- [ ] Loaded server: verify no added latency — `MillisecondsUntilNextTick` returns 0 when timers are firing, sleep is skipped
- [ ] Connect a client during idle — verify connection accepted within one timer tick (~8ms)
- [ ] Verify `[admin` gump shows reasonable CPS values (EMA convergence)
This commit is contained in:
Kamron Batman 2026-03-13 23:53:49 -07:00 • committed by GitHub
parent 1e4cdc4ab6
commit e3cba66284
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4 changed files with 35 additions and 23 deletions
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43
Projects/Server/Main.cs
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@ -110,12 +110,13 @@ public static class Core
public static long Uptime => TickCount - _firstTick;
private static long _cycleIndex;
private static readonly double[] _cyclesPerSecond = new double[128];
private static double _currentCPS;
private static double _averageCPS;
private static bool _cpsInitialized;
public static double CyclesPerSecond => _cyclesPerSecond[_cycleIndex];
public static double CyclesPerSecond => _currentCPS;
public static double AverageCPS => _cyclesPerSecond.Average();
public static double AverageCPS => _averageCPS;
public static string BaseDirectory
{
@ -454,20 +455,12 @@ public static class Core
public static void RunEventLoop()
{
#if DEBUG
const bool isDebugMode = true;
#else
const bool isDebugMode = false;
#endif
var idleCPU = ServerConfiguration.GetSetting("core.enableIdleCPU", isDebugMode);
try
{
var cycleCount = _cyclesPerSecond.Length;
var last = _tickCount;
var lastRaw = Stopwatch.GetTimestamp();
const int interval = 100;
double frequency = Stopwatch.Frequency * interval;
const double alpha = 2.0 / 129; // EMA smoothing (≈128-sample window)
var sample = 0;
@ -504,20 +497,26 @@ public static class Core
if (sample++ == interval)
{
sample = 0;
var now = GetTimestamp();
var nowRaw = Stopwatch.GetTimestamp();
var cyclesPerSecond = frequency / (now - last);
_cyclesPerSecond[_cycleIndex++] = cyclesPerSecond;
if (_cycleIndex == cycleCount)
_currentCPS = frequency / (nowRaw - lastRaw);
if (!_cpsInitialized)
{
_cycleIndex = 0;
_averageCPS = _currentCPS;
_cpsInitialized = true;
}
else
{
_averageCPS += alpha * (_currentCPS - _averageCPS);
}
last = now;
lastRaw = nowRaw;
if (idleCPU && cyclesPerSecond > 125)
var sleepMs = (int)Timer.MillisecondsUntilNextTick(_tickCount);
if (sleepMs >= 2)
{
Thread.Sleep(2);
NetState.WaitForCompletion(sleepMs - 1);
}
}
}