[CentOS-virt] KVM and Windows "/use pmtimer"

Eric Searcy emsearcy at gmail.com
Sat Nov 20 15:12:55 EST 2010


Want to get some more people's opinion on this: the above doc says to use the boot parameter "/use pmtimer" to use the RTC "instead of the TSC for all time sources which resolves guest timing issues".  One: does this have any bearing on whether the host has the constant_tsc flag (i.e. are all the sections that follow "Configuring hosts without a constant Time Stamp Counter" subordinate to it, or does that just have bearing on power management on that one CPU listed---AMD rev F)?

Other question: http://support.microsoft.com/kb/938448 implies that for 2003 SP2 "/use pmtimer" shouldn't be needed as it will use the platform timer (RTC) if you have ACPI or APIC present.  ("By default, Windows Server 2003 Service Pack 2 (SP2) uses the PM timer for all multiprocessor Advanced Programmable Interrupt Controller (APIC) Hardware Abstraction Layers (HALs) or Advanced Configuration and Power Interface (ACPI) HALs".)  Anybody have any experience as to whether this (using ACPI feature in KVM) resolves the timing issues without needing pmtimer explicitly set?


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