提升FastBuild编译UnrealEngine的速度

在上一篇文章之后我进行了进一步测试，下面是结果。

测试结果

测试配置：
i7-8700 3.2Ghz 12线程
16GB内存
WDC PC SN730 SDBQNTY-256G-1001 固态硬盘
ST1000DM003-1SB102 机械硬盘

服务器配置：
Inter Xeon Silver 4114 2.2GHz （2处理器）40线程
64GB内存

引擎版本4.27.0 Release
网络：百兆网络

引擎放在机械硬盘

总共花费时间与编译量：

1>[2328/2328] UnrealBuildTool.exe UE4Editor.target
1>Total time in FASTBuild executor: 8160.80 seconds
1>Total execution time: 8501.83 seconds

141min

引擎放在机械硬盘并禁用插件

总共花费时间与编译量：

3>[1000/1000] UnrealBuildTool.exe UEToonRenderingEditor.target
3>Total time in FASTBuild executor: 3765.71 seconds
3>Total execution time: 3902.75 seconds

65min

这里我额外测试了一下开启ForceRemote的情况:

3>[1000/1000] UnrealBuildTool.exe UEToonRenderingEditor.target
3>Total time in FASTBuild executor: 4508.08 seconds
3>Total execution time: 4708.38 seconds

78min

引擎放在固态硬盘并禁用插件

因为将引擎从机械硬盘移动到固态硬盘，中间删除了一些东西导致引擎多编译了一些，实际时间要比测试的要短3~8min。

3>[1006/1006] UnrealBuildTool.exe UEToonRenderingEditor.target
3>Total time in FASTBuild executor: 2478.80 seconds
3>Total execution time: 2584.69 seconds

43min

猜想与总结

首先FastBuild的大致编译流程为分发编译任务=》远程机编译完之后下载obj文件=》所有编译任务完成后在本地进行链接并且生成对应文件。了解此我们才能对瓶颈进行分析。

• 远程机经常“偷懒”：本人在测试中发现远程机在编译时经常“偷懒”，且该阶段下内存、网络经常处于满负荷状态。因此本人认为这是因为没有使用千兆网络，下载时间过场而导致这种情况的产生。
• 任务显示超时：在编译过程中，远程机有时会出现超时的情况，个人猜测可能是因为动用了所有核心编译，导致网络连接的心跳检测失败而导致的。

基于以上结果我认为以下方法可以提升编译速度，影响程度由高到低排列如下：

1. 在uproject文件中禁用不必要插件。
2. 将源码放在固态硬盘中。
3. 使用千兆网络，而非百兆。（预计能加快5min）
4. 使用缓存模式。

在uproject文件中禁用不必要插件

直接在插件管理界面中禁用插件即可。也可以直接将禁用的列表复制到uproject文件中。本人禁用的插件如下：

"Plugins": [
    {
        "Name": "AlembicImporter",
        "Enabled": false
    },
    {
        "Name": "AppleMoviePlayer",
        "Enabled": false
    },
    {
        "Name": "AppleImageUtils",
        "Enabled": false
    },
    {
        "Name": "OnlineSubsystemGooglePlay",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Android"
        ]
    },
    {
        "Name": "AndroidPermission",
        "Enabled": false
    },
    {
        "Name": "AndroidMoviePlayer",
        "Enabled": false
    },
    {
        "Name": "AndroidMedia",
        "Enabled": false
    },
    {
        "Name": "AndroidDeviceProfileSelector",
        "Enabled": false
    },
    {
        "Name": "AudioCapture",
        "Enabled": false
    },
    {
        "Name": "AutomationUtils",
        "Enabled": false
    },
    {
        "Name": "AvfMedia",
        "Enabled": false
    },
    {
        "Name": "ChaosClothEditor",
        "Enabled": false
    },
    {
        "Name": "ChaosCloth",
        "Enabled": false
    },
    {
        "Name": "ChaosEditor",
        "Enabled": false
    },
    {
        "Name": "ChaosNiagara",
        "Enabled": false
    },
    {
        "Name": "ChaosSolverPlugin",
        "Enabled": false
    },
    {
        "Name": "CodeLiteSourceCodeAccess",
        "Enabled": false
    },
    {
        "Name": "CLionSourceCodeAccess",
        "Enabled": false
    },
    {
        "Name": "Paper2D",
        "Enabled": false
    },
    {
        "Name": "GooglePAD",
        "Enabled": false
    },
    {
        "Name": "MagicLeapMedia",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Lumin"
        ]
    },
    {
        "Name": "MagicLeap",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Lumin",
            "Mac",
            "Win64"
        ]
    },
    {
        "Name": "MagicLeapPassableWorld",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Lumin",
            "Mac",
            "Win64"
        ]
    },
    {
        "Name": "OpenImageDenoise",
        "Enabled": false
    },
    {
        "Name": "IOSDeviceProfileSelector",
        "Enabled": false
    },
    {
        "Name": "LinuxDeviceProfileSelector",
        "Enabled": false
    },
    {
        "Name": "CharacterAI",
        "Enabled": false
    },
    {
        "Name": "DatasmithContent",
        "Enabled": false
    },
    {
        "Name": "GeometryCache",
        "Enabled": false
    },
    {
        "Name": "SpeedTreeImporter",
        "Enabled": false
    },
    {
        "Name": "LuminPlatformFeatures",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Lumin"
        ]
    },
    {
        "Name": "MLSDK",
        "Enabled": false
    },
    {
        "Name": "WmfMedia",
        "Enabled": false
    },
    {
        "Name": "WebMMoviePlayer",
        "Enabled": false
    },
    {
        "Name": "MediaCompositing",
        "Enabled": false
    },
    {
        "Name": "ImgMedia",
        "Enabled": false
    },
    {
        "Name": "OnlineSubsystemNull",
        "Enabled": false
    },
    {
        "Name": "OnlineSubsystemUtils",
        "Enabled": false
    },
    {
        "Name": "OnlineSubsystemIOS",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "IOS",
            "TVOS"
        ]
    },
    {
        "Name": "ChunkDownloader",
        "Enabled": false
    },
    {
        "Name": "OnlineSubsystem",
        "Enabled": false
    },
    {
        "Name": "XCodeSourceCodeAccess",
        "Enabled": false
    },
    {
        "Name": "EditableMesh",
        "Enabled": false
    },
    {
        "Name": "PerforceSourceControl",
        "Enabled": false
    },
    {
        "Name": "PlasticSourceControl",
        "Enabled": false
    },
    {
        "Name": "SubversionSourceControl",
        "Enabled": false
    },
    {
        "Name": "SteamVR",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Win32",
            "Win64",
            "Linux"
        ]
    },
    {
        "Name": "OpenXRHandTracking",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Win32",
            "Win64",
            "Linux",
            "HoloLens",
            "Android"
        ]
    },
    {
        "Name": "OpenXREyeTracker",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Win32",
            "Win64",
            "Linux",
            "HoloLens",
            "Android"
        ]
    },
    {
        "Name": "OpenXR",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Win32",
            "Win64",
            "Linux",
            "Android",
            "HoloLens"
        ]
    },
    {
        "Name": "OculusVR",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "Win32",
            "Win64",
            "Android"
        ]
    },
    {
        "Name": "EnvironmentQueryEditor",
        "Enabled": false
    },
    {
        "Name": "AISupport",
        "Enabled": false
    },
    {
        "Name": "Synthesis",
        "Enabled": false
    },
    {
        "Name": "MotoSynth",
        "Enabled": false
    },
    {
        "Name": "SoundFields",
        "Enabled": false
    },
    {
        "Name": "LocationServicesBPLibrary",
        "Enabled": false
    },
    {
        "Name": "XGEController",
        "Enabled": false
    },
    {
        "Name": "OodleData",
        "Enabled": false
    },
    {
        "Name": "OodleNetwork",
        "Enabled": false
    },
    {
        "Name": "TextureFormatOodle",
        "Enabled": false
    },
    {
        "Name": "ExampleDeviceProfileSelector",
        "Enabled": false
    },
    {
        "Name": "GeometryMode",
        "Enabled": false
    },
    {
        "Name": "MeshPainting",
        "Enabled": false
    },
    {
        "Name": "TcpMessaging",
        "Enabled": false
    },
    {
        "Name": "UdpMessaging",
        "Enabled": false
    },
    {
        "Name": "MacGraphicsSwitching",
        "Enabled": false
    },
    {
        "Name": "MobileLauncherProfileWizard",
        "Enabled": false
    },
    {
        "Name": "PlatformCrypto",
        "Enabled": false
    },
    {
        "Name": "MobilePatchingUtils",
        "Enabled": false
    },
    {
        "Name": "WindowsMoviePlayer",
        "Enabled": false
    },
    {
        "Name": "GoogleCloudMessaging",
        "Enabled": false
    },
    {
        "Name": "PhysXVehicles",
        "Enabled": false
    },
    {
        "Name": "NullSourceCodeAccess",
        "Enabled": false
    },
    {
        "Name": "FacialAnimation",
        "Enabled": false
    },
    {
        "Name": "PostSplashScreen",
        "Enabled": false,
        "SupportedTargetPlatforms": [
            "XboxOne"
        ]
    },
    {
        "Name": "KDevelopSourceCodeAccess",
        "Enabled": false
    },
    {
        "Name": "MatineeToLevelSequence",
        "Enabled": false
    },
    {
        "Name": "MediaPlayerEditor",
        "Enabled": false
    },
    {
        "Name": "VisualStudioCodeSourceCodeAccess",
        "Enabled": false
    }
]

其实还可以禁用更多的插件，我在测试的时候没有全部禁用。
除了可以减少编译量，以节约时间外。同时也可以减少编译完之后所占用的空间。占用空间165G=>108G。

使用缓存模式

经过测试仅仅是将bEnableCaching设置为true好像是不能开启缓存模式的。应该还需要设置CacheMode。在源码中CacheMode分别为ReadWrite、ReadOnly、WriteOnly,枚举对应的值依次为0,1,2。因为缓存模式适用于多人引擎团队，对于我这种独狼爱好者来说意义不大，所以就没测试。有兴趣的可以自己跟一下UBT的代码。

<FASTBuild>
    <bEnableCaching>true</bEnableCaching>
    <CacheMode>0</CacheMode>
</FASTBuild>

本地核心控制

在编译UE4时FastBuildWorker.exe无法控制本地使用核心数。如果你不想占用本地资源可以将bForceRemote设置为true,引擎编译过程中就不会占用本地核心了（开头还是会使用一些，以及Link阶段只能进行）。

如果只想让本地不会卡死，则可以使用一下参数：

<LocalExecutor>
    <ProcessorCountMultiplier>0.9</ProcessorCountMultiplier>
    <MaxProcessorCount>11</MaxProcessorCount>
</LocalExecutor>
<ParallelExecutor>
    <ProcessorCountMultiplier>0.9</ProcessorCountMultiplier>
    <MaxProcessorCount>11</MaxProcessorCount>
</ParallelExecutor>

本人测试结果，不设置MaxProcessorCount是不行的。