Windows 7: Designing Efficient Background Processes

1. PC19 Windows 7: Designing Efficient Background Processes Vikram Singh Program Manager Microsoft Corporation

2. Agenda • Introduction • Choosing the Right Model • Windows 7 Trigger-Start Services • Task Scheduler Conditions and Triggers • Security and Performance Recommendations

3. What Is Background Activity? • System activity that is not directly initiated by user • Services, Scheduled tasks, some COM processes such as a COM service, WMI providers, etc. • Part of nearly every usage scenario: • Search indexing • System security and maintenance • Network management • Device management • System configuration

4. Performance • Responsiveness to the user • Consumes resources from foreground applications • Boot, Shutdown, Logoff, etc. • Reliability • Memory leaks • System crashes, hangs • Dependent application crashes Impact Of Background Activity • Security • Activity may require system privileges • Successful attack may compromise entire system • Power Consumption • Extra disk, CPU utilization • Decrease in battery life • Prevents idle efficiencies

5. Impact Of Background Activity • Internal evaluation of 49 Windows services • Not critical for boot and login • Critical and required for their individual scenarios

6. Background Activity Performance Impact • Compared IT image to clean Windows Vista installation: • 10 additional 3rd-party services

7. Designing For Efficiency • Choose the right model • Windows Service or Scheduled Task? • Leverage the latest Windows infrastructure • Trigger-Start Services for Windows 7 • Make performance optimizations • Eliminate unnecessary privileges • Evaluate and measure • Iterate (step 1)

8. Services And Scheduled Tasks • Continuous activity from boot to shutdown • Service Control Manager (SCM) programming model • Can specify dependency • Short duration action • Idle activity • Take action on user login • Standalone executable or out-of-process COM server • Generally execute in user session • Windows Service • Scheduled Task

9. Windows Services: Auto_Start • Auto_Startstart type enables the service to launch at boot and never terminate • Most common service start type • Easy for developers—service is always running! • Problems • Startup time adds to boot time • Adds to system base “footprint” • Many Auto_Start services wait for rare events

10. Windows 7: Trigger-Start Services • Trigger-Start centralizes environmental detection logic • SCM registers for system events via interesting providers: • Device arrival • IP address • Domain join and leave • Group policy updates • Custom ETW (Event Tracing for Windows) events • SCM starts or stops registered services: • Examples: • TabletInputService started only if digitizer is present • StorSvc starts when group policy updates are applied, automatically stops

11. demo Converting a Service to Trigger-Start

12. SomeTrigger-Start Services In Windows 7 • Windows 7 (Build 6801)

13. Service Shutdown • Self-stop the service • Immediately or after pre-determined idle time when task is complete if Trigger-StartorDemand_Start • System shutdown • Do not set SERVICE_ACCEPT_SHUTDOWN unless required • No need to free memory if the service is in a standalone process • Target less than 200ms for completing shutdown notification

14. Service Control Handler • No blocking calls! • WaitForSingleObject, CreateFile, RPCs, etc. • Strive for lock-free code • Execute work items in a thread pool • Follow the MSDN guidelines for specific return codes • SERVICE_CONTROL_STOP • Call SetServiceStatus(SERVICE_STOP_PENDING) • Post stop work to a thread pool • Order is key!

15. Service Security • [DllImport(“advapi32.dll”, SetLastError=true)] • Public static extern bool ChangeServiceConfig2( • IntPtrhService, • uint32dwInfoLevel, • IntPtrlpInfo • ); • Const uint32 SERVICE_CONFIG_REQUIRED_PRIVILEGES_INFO = 6 • // Example UPS Service • protected override void OnStart (string[] args) • { • IntPtrServiceHandle; • IntPtrRequiredPrivilegesString; • // set required privileges • string RequiredPrivileges = “SeShutdownPrivilege\0\0”; • RequiredPrivilegesString = Marshal.StringToHGlobalAuto(RequiredPrivileges); • ChangeServiceConfig2( • this.ServiceHandle, • SERVICE_CONFIG_REQUIRED_PRIVILEGES_INFO, • RequiredPrivilegesString • ); • } • Run in the least privilege required • LocalService/NetworkService • Avoid LocalSystem • Remove unneeded privileges • E.g., SeImpersonatePrivilege • Express required privileges • SCM automatically removes all others

16. Scheduled Tasks

17. Scheduled Task Example • Power Efficiency Diagnostics • Windows 7 power problem analysis • Executes every 2 weeks when the system is idle • Requires SYSTEM privilege to access NT Kernel Logger • Saves report data for user • Uploads CEIP data to Microsoft Kernel Detects Idle Condition Task Scheduler (schedule) Launches Task Power Efficiency Diagnostics (powercfg.exe)

18. Task Triggers • Calendar • Boot • Logon • Idle • Event log based entry • Workstation lock • Workstation unlock

19. Task Conditions • Idle condition • Stop when not idle • AC power only • Stop on battery • Wake computer from sleep • Specific or any network connection

20. Task Recommendations • Use the idle condition to prevent background activity from interrupting the user • Enable the Power condition—do not run when the system is on battery • Enable the Network condition if the task requires network connectivity • E.g., download software update

21. Performance And Power • Performance is critical for background activity • Adds to the base footprint of the system • Interferes with foreground user activity • Resource utilization directly tied to Power Consumption • Target: • Less than 2% CPU activity when the system is idle • No disk activity when the system is idle • Evaluate and Measure: • Use XPerf (Windows Performance Tools Kit)

22. Call To Action • Understand that background activity has tangible impact on system quality • Select the right model: service or task • Use Windows 7 Trigger-Start instead of Auto_Start • Configure your service to use the smallest set of security privileges • Leverage scheduled task idle, power and network conditions • Use Windows Performance Tools Kit (XPerf) to measure

23. Additional Resources • Developing Efficient Background Processes for Windows • http://go.microsoft.com/fwlink/?LinkId=128622 • Services in Windows Vista • http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/Vista_Services.doc • Service Control Manager [MSDN] • http://msdn.microsoft.com/en-us/library/ms685150(VS.85).aspx • Task Scheduler • http://msdn.microsoft.com/en-us/library/aa383614.aspx • Windows Performance Tools Kit • http://www.microsoft.com/whdc/system/sysperf/perftools.mspx

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