Timekeeping in VMware Virtual Machines VMware vSphere 5.0, Workstation 8.0, Fusion 4.0 INFORMA TION GUIDE Timekeeping in VMware Virtual Machines VMware vSphere 5.0, Workstation 8.0, Fusion 4.0 Table of Contents Introduction .................................................................................................................................................................................................................. 4 Timekeeping Basics ................................................................................................................................................................................................... 4 Tick Counting ........................................................................................................................................................................................................ 4 Tickless Timekeeping......................................................................................................................................................................................... 5 Initializing and Correcting Wall-Clock Time ............................................................................................................................................ 6 PC Timer Hardware ................................................................................................................................................................................................... 6 PIT ............................................................................................................................................................................................................................... 7 CMOS RTC .............................................................................................................................................................................................................. 8 Local APIC Timer ................................................................................................................................................................................................. 8 ACPI Timer .............................................................................................................................................................................................................. 8 TSC ............................................................................................................................................................................................................................. 8 HPET .......................................................................................................................................................................................................................... 9 VMware Timer Virtualization ................................................................................................................................................................................. 9 Virtual PIT ................................................................................................................................................................................................................ 9 Virtual CMOS RTC ............................................................................................................................................................................................. 10 Virtual Local APIC Timer ................................................................................................................................................................................. 11 Virtual ACPI Timer ............................................................................................................................................................................................. 11 Virtual TSC ............................................................................................................................................................................................................. 11 Pseudoperformance Counters .................................................................................................................................................................... 13 Virtual HPET ......................................................................................................................................................................................................... 13 Other Time-Dependent Devices ................................................................................................................................................................. 13 VMI Paravirtual Timer ...................................................................................................................................................................................... 14 Timekeeping in Specific Operating Systems ............................................................................................................................................... 14 Microsoft Windows ........................................................................................................................................................................................... 14 Linux ........................................................................................................................................................................................................................ 15 Kernels Before Clocksource.................................................................................................................................................................... 16 Clocksource Kernels ................................................................................................................................................................................... 18 Paravirtual Kernels ...................................................................................................................................................................................... 18 Solaris...................................................................................................................................................................................................................... 18 Synchronizing Virtual Machines and Hosts with Real Time .................................................................................................................. 19 Using VMware Tools Clock Synchronization ....................................................................................................................................... 20 Enabling Periodic Synchronization .................................................................................................................................................... 20 Disabling All Synchronization ............................................................................................................................................................... 21 Using Microsoft W32Time in Windows Guests .................................................................................................................................. 22 Using NTP in Linux and Other Guests ..................................................................................................................................................... 23 Host Clock Synchronization ........................................................................................................................................................................ 23 Time and Performance Measurements Within a Virtual Machine ..................................................................................................... 24 Time Measurements ........................................................................................................................................................................................ 24 Performance Measurements ....................................................................................................................................................................... 24 Event Counts ...................................................................................................................................................................................................... 25 Memory Usage ................................................................................................................................................................................................... 25 CPU Usage ........................................................................................................................................................................................................... 25 INFORMATION GUIDE /2 Timekeeping in VMware Virtual Machines VMware vSphere 5.0, Workstation 8.0, Fusion 4.0 Resource Pressure ................................................................................................................................................................................................... 26 CPU Pressure ...................................................................................................................................................................................................... 26 Memory Pressure .............................................................................................................................................................................................