Bug 838061

Summary: Set USE_PLATFORM_CLOCK bit in FADT
Product: Red Hat Enterprise Linux 7 Reporter: Marcelo Tosatti <mtosatti>
Component: seabiosAssignee: Marcelo Tosatti <mtosatti>
Status: CLOSED NOTABUG QA Contact: Virtualization Bugs <virt-bugs>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.0CC: juzhang, tburke, virt-maint, xfu
Target Milestone: rc   
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Hardware: Unspecified   
OS: Unspecified   
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2012-11-29 00:42:03 UTC Type: Bug
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Marcelo Tosatti 2012-07-06 10:55:33 UTC
The Virtualization Host Configuration and Guest Installation Guide (http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/chap-Virtualization_Host_Configuration_and_Guest_Installation_Guide-KVM_guest_timing_management.html) mentions that

"Using the Real-Time Clock with Windows Vista, Windows Server 2008 and Windows 7 guests
Windows uses the both the Real-Time Clock (RTC) and the Time Stamp Counter (TSC). For Windows guests the Real-Time Clock can be used instead of the TSC for all time sources which resolves guest timing issues."

Use of platform clock should be mandatory, not optional. This is possible by setting the USE_PLATFORM_CLOCK bit (bit 15) in the FADT:

"A value of one indicates that OSPM should use a platform provided timer to drive any monotonically non-decreasing counters, such as OSPM performance counter services."

More information at 

http://blogs.technet.com/b/perfguru/archive/2008/02/18/explanation-for-the-usepmtimer-switch-in-the-boot-ini.aspx

Comment 3 Marcelo Tosatti 2012-11-29 00:42:03 UTC
Seabios from rhel7 already includes said bit.