From 1be668e68a1937f2af239e2707ab914286018892 Mon Sep 17 00:00:00 2001
From: riperiperi <rhy3756547@hotmail.com>
Date: Thu, 30 Nov 2023 10:39:42 -0800
Subject: HLE: Add OS-specific precise sleep methods to reduce spinwaiting
 (#5948)

* feat: add nanosleep for linux and macos

* Add Windows 0.5ms sleep

- Imprecise waits for longer waits with clock alignment
- 1/4 the spin time on vsync timer

* Remove old experiment

* Fix event leak

* Tweaking for MacOS

* Linux tweaks, nanosleep vsync improvement

* Fix overbias

* Cleanup

* Fix realignment

* Add some docs and some cleanup

NanosleepPool needs more, Nanosleep has some benchmark code that needs removed.

* Rename "Microsleep" to "PreciseSleep"

Might have been confused with "microseconds", which no measurement is performed in.

* Remove nanosleep measurement

* Remove unused debug logging

* Nanosleep Pool Documentation

* More cleanup

* Whitespace

* Formatting

* Address Feedback

* Allow SleepUntilTimePoint to take EventWaitHandle

* Remove `_chrono` stopwatch in SurfaceFlinger

* Move spinwaiting logic to PreciseSleepHelper

Technically, these achieve different things, but having them here makes them easier to reuse or tune.
---
 .../PreciseSleep/WindowsSleepEvent.cs              | 92 ++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 src/Ryujinx.Common/PreciseSleep/WindowsSleepEvent.cs

(limited to 'src/Ryujinx.Common/PreciseSleep/WindowsSleepEvent.cs')

diff --git a/src/Ryujinx.Common/PreciseSleep/WindowsSleepEvent.cs b/src/Ryujinx.Common/PreciseSleep/WindowsSleepEvent.cs
new file mode 100644
index 00000000..87c10d18
--- /dev/null
+++ b/src/Ryujinx.Common/PreciseSleep/WindowsSleepEvent.cs
@@ -0,0 +1,92 @@
+using Ryujinx.Common.SystemInterop;
+using System;
+using System.Runtime.Versioning;
+using System.Threading;
+
+namespace Ryujinx.Common.PreciseSleep
+{
+    /// <summary>
+    /// A precise sleep event that uses Windows specific methods to increase clock resolution beyond 1ms,
+    /// use the clock's phase for more precise waits, and potentially align timepoints with it.
+    /// </summary>
+    [SupportedOSPlatform("windows")]
+    internal class WindowsSleepEvent : IPreciseSleepEvent
+    {
+        /// <summary>
+        /// The clock can drift a bit, so add this to encourage the clock to still wait if the next tick is forecasted slightly before it.
+        /// </summary>
+        private const long ErrorBias = 50000;
+
+        /// <summary>
+        /// Allowed to be 0.05ms away from the clock granularity to reduce precision.
+        /// </summary>
+        private const long ClockAlignedBias = 50000;
+
+        /// <summary>
+        /// The fraction of clock granularity above the timepoint that will align it down to the lower timepoint.
+        /// Currently set to the lower 1/4, so for 0.5ms granularity: 0.1ms would be rounded down, 0.2 ms would be rounded up.
+        /// </summary>
+        private const long ReverseTimePointFraction = 4;
+
+        private readonly AutoResetEvent _waitEvent = new(false);
+        private readonly WindowsGranularTimer _timer = WindowsGranularTimer.Instance;
+
+        /// <summary>
+        /// Set to true to disable timepoint realignment.
+        /// </summary>
+        public bool Precise { get; set; } = false;
+
+        public long AdjustTimePoint(long timePoint, long timeoutNs)
+        {
+            if (Precise || timePoint == long.MaxValue)
+            {
+                return timePoint;
+            }
+
+            // Does the timeout align with the host clock?
+
+            long granularity = _timer.GranularityNs;
+            long misalignment = timeoutNs % granularity;
+
+            if ((misalignment < ClockAlignedBias || misalignment > granularity - ClockAlignedBias) && timeoutNs > ClockAlignedBias)
+            {
+                // Inaccurate sleep for 0.5ms increments, typically.
+
+                (long low, long high) = _timer.ReturnNearestTicks(timePoint);
+
+                if (timePoint - low < _timer.GranularityTicks / ReverseTimePointFraction)
+                {
+                    timePoint = low;
+                }
+                else
+                {
+                    timePoint = high;
+                }
+            }
+
+            return timePoint;
+        }
+
+        public bool SleepUntil(long timePoint)
+        {
+            return _timer.SleepUntilTimePoint(_waitEvent, timePoint + (ErrorBias * PerformanceCounter.TicksPerMillisecond) / 1_000_000);
+        }
+
+        public void Sleep()
+        {
+            _waitEvent.WaitOne();
+        }
+
+        public void Signal()
+        {
+            _waitEvent.Set();
+        }
+
+        public void Dispose()
+        {
+            GC.SuppressFinalize(this);
+
+            _waitEvent.Dispose();
+        }
+    }
+}
-- 
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