tools: event-loop measurement harness

The A/B harness used to measure the idle-sleep work that shipped in main (#2559): Measure-EventLoop.ps1 and measure-event-loop.sh drive CPU/lag comparisons across server.eventLoopIdleWaitMs settings, and HostLatencyProbe.cs measures what basic operations cost on a host. dev-docs/measuring-event-loop.md explains the method, the numbers that matter, and how to re-vendor IORingGroup for ring experiments. This branch is main plus this commit, rebased forward as main moves. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-08-09 13:35:41 -07:00 · 2026-08-09 13:35:41 -07:00 · e09bd6ea71
commit e09bd6ea71
parent 6d846b11e5
6 changed files with 581 additions and 0 deletions
--- a/tools/Measure-EventLoop.ps1
+++ b/tools/Measure-EventLoop.ps1
@ -0,0 +1,96 @@
+# A/B measurement for the event loop scheduler.
+#
+# Boots the shard twice against identical binaries -- once with idle sleeping disabled
+# (server.eventLoopIdleWaitMs = 0) and once with idle sleeping (= 2) -- and samples process CPU
+# time over a fixed window. Everything else is held constant, so the delta is the scheduler.
+#
+# Usage:  pwsh tools/Measure-EventLoop.ps1 [-WarmupSeconds 45] [-SampleSeconds 60]
+
+param(
+    [int]$WarmupSeconds = 45,
+    [int]$SampleSeconds = 60
+)
+
+$ErrorActionPreference = 'Stop'
+
+$root = Split-Path -Parent $PSScriptRoot
+$dist = Join-Path $root 'Distribution'
+$exe = Join-Path $dist 'ModernUO.exe'
+$configPath = Join-Path $dist 'Configuration\modernuo.json'
+
+if (-not (Test-Path $exe)) {
+    throw "ModernUO.exe not found at $exe. Build with: dotnet build -c Release"
+}
+
+function Set-IdleWait([int]$value) {
+    $json = Get-Content $configPath -Raw | ConvertFrom-Json
+    $json.settings.'server.eventLoopIdleWaitMs' = "$value"
+    $json | ConvertTo-Json -Depth 20 | Set-Content $configPath -Encoding UTF8
+}
+
+function Measure-Loop([int]$idleWait, [string]$label) {
+    Set-IdleWait $idleWait
+
+    Write-Host ""
+    Write-Host "=== $label (server.eventLoopIdleWaitMs = $idleWait) ===" -ForegroundColor Cyan
+
+    # Redirect stdin from an empty file so the server runs headless and never blocks on console
+    # input. PowerShell cannot redirect from NUL, so an actual empty file stands in for it.
+    $stdin = Join-Path $dist 'empty.in'
+    if (-not (Test-Path $stdin)) {
+        Set-Content -Path $stdin -Value '' -NoNewline
+    }
+
+    $proc = Start-Process -FilePath $exe -WorkingDirectory $dist -PassThru `
+        -RedirectStandardInput $stdin `
+        -RedirectStandardOutput (Join-Path $dist "Logs\measure-$idleWait.out") `
+        -RedirectStandardError  (Join-Path $dist "Logs\measure-$idleWait.err")
+
+    try {
+        Write-Host "  pid $($proc.Id); warming up for ${WarmupSeconds}s..."
+        Start-Sleep -Seconds $WarmupSeconds
+
+        if ($proc.HasExited) {
+            throw "Server exited during warmup (code $($proc.ExitCode)). See Logs\measure-$idleWait.err"
+        }
+
+        $proc.Refresh()
+        $cpuBefore = $proc.TotalProcessorTime
+        $wallBefore = Get-Date
+
+        Write-Host "  sampling for ${SampleSeconds}s..."
+        Start-Sleep -Seconds $SampleSeconds
+
+        $proc.Refresh()
+        $cpuAfter = $proc.TotalProcessorTime
+        $wallAfter = Get-Date
+
+        $cpuMs = ($cpuAfter - $cpuBefore).TotalMilliseconds
+        $wallMs = ($wallAfter - $wallBefore).TotalMilliseconds
+        $pct = $cpuMs / $wallMs * 100
+
+        Write-Host ("  CPU: {0:F2}% of one core  ({1:F0}ms CPU over {2:F0}ms wall)" -f $pct, $cpuMs, $wallMs) -ForegroundColor Yellow
+
+        [pscustomobject]@{ Label = $label; IdleWait = $idleWait; CpuPercent = $pct }
+    }
+    finally {
+        if (-not $proc.HasExited) {
+            $proc.Kill()
+            $proc.WaitForExit(10000) | Out-Null
+        }
+    }
+}
+
+$legacy = Measure-Loop 0 'Never sleep (max responsiveness)'
+$sleeping = Measure-Loop 2 'Idle sleeping'
+
+Write-Host ""
+Write-Host "=== Result ===" -ForegroundColor Green
+Write-Host ("  never sleep : {0,6:F2}% of one core" -f $legacy.CpuPercent)
+Write-Host ("  idle sleep  : {0,6:F2}% of one core" -f $sleeping.CpuPercent)
+if ($sleeping.CpuPercent -gt 0) {
+    Write-Host ("  reduction   : {0,6:F1}x" -f ($legacy.CpuPercent / $sleeping.CpuPercent))
+}
+
+# Leave the config on the new behaviour.
+Set-IdleWait 2