zgc-jdk25-benchmarks/scripts/run-all.ps1

<#
.SYNOPSIS
  Compiles and runs the whole ZGC-vs-G1 suite, writing every raw output into results/.

.DESCRIPTION
  Every number published in the companion blog post comes from this script. It is deliberately
  boring and sequential: GC benchmarks that run concurrently with each other measure the scheduler.

.PARAMETER JavaHome
  Path to a JDK 25 (or newer) installation. Generational ZGC is the only ZGC from JDK 24 onward.

.EXAMPLE
  pwsh scripts/run-all.ps1 -JavaHome 'C:\Program Files\Java\jdk-25.0.3'
#>
param(
    [string]$JavaHome = $env:JAVA_HOME,
    [string]$MavenHome = "$HOME\ankurm-blog-tools\apache-maven-3.9.9",
    [int]$MeasureSeconds = 60,
    [int]$WarmupSeconds = 20,
    [switch]$SkipJmh
)

$ErrorActionPreference = 'Stop'
if (-not $JavaHome) { throw "Set -JavaHome or JAVA_HOME to a JDK 25+ installation." }

$Root    = Split-Path -Parent $PSScriptRoot
$Java    = Join-Path $JavaHome 'bin\java.exe'
$Javac   = Join-Path $JavaHome 'bin\javac.exe'
$Out     = Join-Path $Root 'out'
$Results = Join-Path $Root 'results'
$Logs    = Join-Path $Root 'logs'

New-Item -ItemType Directory -Force -Path $Out, $Results, $Logs | Out-Null

# Fixed heap for every run. -Xms == -Xmx removes heap resizing as a variable; a benchmark that lets
# the heap grow during measurement is partly measuring the resize policy.
$Heap = @('-Xms2g', '-Xmx2g')

Write-Host "==> compiling" -ForegroundColor Cyan
$sources = Get-ChildItem "$Root\latency\src", "$Root\tuning\src", "$Root\internals\src", "$Root\analysis\src" `
           -Recurse -Filter *.java -ErrorAction SilentlyContinue | ForEach-Object { $_.FullName }
& $Javac -d $Out @sources
if ($LASTEXITCODE -ne 0) { throw "compilation failed" }

# NOTE: several of these commands (notably `java -version` and `-XX:+PrintFlagsFinal`) write to
# stderr. PowerShell turns native stderr into error records, and with $ErrorActionPreference='Stop'
# that aborts the whole script on a perfectly successful run. Routing through cmd.exe with a plain
# 2>&1 merge keeps stderr as text where it belongs.
function Invoke-Capture {
    param([string]$Name, [string[]]$JvmArgs, [string[]]$AppArgs)
    $file = Join-Path $Results "$Name.txt"
    Write-Host "==> $Name" -ForegroundColor Cyan
    $quoted = @("`"$Java`"") + ($JvmArgs + $AppArgs | ForEach-Object {
        if ($_ -match '[\s]') { "`"$_`"" } else { $_ }
    })
    $line = ($quoted -join ' ')
    $output = cmd /c "$line 2>&1"
    $output | Out-File -FilePath $file -Encoding utf8
    $output | Select-Object -Last 6 | ForEach-Object { Write-Host "    $_" -ForegroundColor DarkGray }
    Write-Host "    -> results/$Name.txt" -ForegroundColor DarkGray
}

# ---------------------------------------------------------------------------------------------
# 1. Environment -- printed once per collector so the results file is self-describing.
# ---------------------------------------------------------------------------------------------
Invoke-Capture -Name '01-env-zgc' -JvmArgs (@('-XX:+UseZGC')  + $Heap) -AppArgs @("$Root\env\Env.java")
Invoke-Capture -Name '01-env-g1'  -JvmArgs (@('-XX:+UseG1GC') + $Heap) -AppArgs @("$Root\env\Env.java")

Invoke-Capture -Name '02-flags-zgc' -JvmArgs (@('-XX:+UseZGC')  + $Heap + @('-XX:+PrintFlagsFinal')) -AppArgs @('-version')
Invoke-Capture -Name '02-flags-g1'  -JvmArgs (@('-XX:+UseG1GC') + $Heap + @('-XX:+PrintFlagsFinal')) -AppArgs @('-version')

# ---------------------------------------------------------------------------------------------
# 2. Open-loop latency, with full unified GC logging written alongside.
# ---------------------------------------------------------------------------------------------
$latencyProps = @("-DwarmupSeconds=$WarmupSeconds", "-Dseconds=$MeasureSeconds")

Invoke-Capture -Name '03-latency-zgc' `
    -JvmArgs (@('-XX:+UseZGC') + $Heap + $latencyProps + @("-Xlog:gc*,gc+heap=debug:file=$Logs\zgc-latency.log:time,uptime,level,tags")) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.latency.LatencyHarness')

Invoke-Capture -Name '03-latency-g1' `
    -JvmArgs (@('-XX:+UseG1GC') + $Heap + $latencyProps + @("-Xlog:gc*,gc+heap=debug:file=$Logs\g1-latency.log:time,uptime,level,tags")) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.latency.LatencyHarness')

# ---------------------------------------------------------------------------------------------
# 3. Allocation stalls -- deliberately undersized heap. This is the section most GC posts skip.
# ---------------------------------------------------------------------------------------------
$stallHeap = @('-Xms512m', '-Xmx512m')

Invoke-Capture -Name '04-stalls-zgc-baseline' `
    -JvmArgs (@('-XX:+UseZGC') + $stallHeap + @('-Dseconds=20')) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.tuning.AllocationStallDemo')

Invoke-Capture -Name '04-stalls-zgc-softmax' `
    -JvmArgs (@('-XX:+UseZGC', '-XX:SoftMaxHeapSize=400m') + $stallHeap + @('-Dseconds=20')) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.tuning.AllocationStallDemo')

Invoke-Capture -Name '04-stalls-zgc-spiketolerance' `
    -JvmArgs (@('-XX:+UseZGC', '-XX:ZAllocationSpikeTolerance=5') + $stallHeap + @('-Dseconds=20')) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.tuning.AllocationStallDemo')

# The same stress under G1: ZGC's stalls become G1's evacuation failures and Full GCs.
Invoke-Capture -Name '04-stalls-g1' `
    -JvmArgs (@('-XX:+UseG1GC') + $stallHeap + @('-Dseconds=20', "-Xlog:gc:file=$Logs\g1-stress.log:time,uptime")) `
    -AppArgs @('-cp', $Out, 'com.ankurm.zgc.tuning.AllocationStallDemo')

# ---------------------------------------------------------------------------------------------
# 4. Page-size / humongous behaviour.
# ---------------------------------------------------------------------------------------------
Invoke-Capture -Name '05-pages-zgc' `
    -JvmArgs (@('-XX:+UseZGC') + $Heap) -AppArgs @('-cp', $Out, 'com.ankurm.zgc.internals.PageSizeDemo')
Invoke-Capture -Name '05-pages-g1' `
    -JvmArgs (@('-XX:+UseG1GC') + $Heap) -AppArgs @('-cp', $Out, 'com.ankurm.zgc.internals.PageSizeDemo')

# ---------------------------------------------------------------------------------------------
# 5. GC log analysis -- turns the raw unified logs above into pause distributions.
# ---------------------------------------------------------------------------------------------
Invoke-Capture -Name '06-gclog-zgc' -JvmArgs @() -AppArgs @('-cp', $Out, 'com.ankurm.zgc.analysis.GcLogParser', "$Logs\zgc-latency.log")
Invoke-Capture -Name '06-gclog-g1'  -JvmArgs @() -AppArgs @('-cp', $Out, 'com.ankurm.zgc.analysis.GcLogParser', "$Logs\g1-latency.log")

# ---------------------------------------------------------------------------------------------
# 6. JMH throughput / barrier microbenchmarks.
# ---------------------------------------------------------------------------------------------
if (-not $SkipJmh) {
    Write-Host "==> building JMH module" -ForegroundColor Cyan
    Push-Location "$Root\jmh"
    $env:JAVA_HOME = $JavaHome
    & (Join-Path $MavenHome 'bin\mvn.cmd') -q -B clean package
    Pop-Location

    foreach ($gc in @('UseZGC', 'UseG1GC')) {
        $tag = if ($gc -eq 'UseZGC') { 'zgc' } else { 'g1' }
        # IMPORTANT: the GC flag must go in -jvmArgs. JMH forks a fresh JVM for every trial, and a
        # GC flag on the outer `java -jar` command is NOT inherited by the fork. Getting this wrong
        # is the single most common way to publish a GC benchmark that measured the default GC twice.
        Invoke-Capture -Name "07-jmh-$tag" -JvmArgs @('-jar', "$Root\jmh\target\benchmarks.jar") `
            -AppArgs @('-jvmArgs', "-XX:+$gc -Xms2g -Xmx2g", '-prof', 'gc', '-rf', 'json',
                       '-rff', "$Results\07-jmh-$tag.json")
    }
}

Write-Host ""
Write-Host "All raw output is in $Results" -ForegroundColor Green