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Bug 865315 - RFE: use -rtc driftfix=slew
RFE: use -rtc driftfix=slew
Product: Red Hat OpenStack
Classification: Red Hat
Component: RFEs (Show other bugs)
Unspecified Unspecified
unspecified Severity medium
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Assigned To: Alan Pevec
Yaniv Kaul
: FutureFeature
Depends On:
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Reported: 2012-10-11 04:17 EDT by Yaniv Kaul
Modified: 2013-07-03 22:52 EDT (History)
3 users (show)

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Doc Type: Enhancement
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Last Closed: 2012-10-11 11:48:45 EDT
Type: Bug
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RHEL 7.3 requirements from Atomic Host:
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Description Yaniv Kaul 2012-10-11 04:17:23 EDT
Description of problem:
I'm not sure what the default downstream of driftfix is, but it should be slew to prevent Windows from BSOD.

RHEV/oVirt sets this option in the QEMU command line.

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Comment 2 Daniel Berrange 2012-10-11 11:48:45 EDT
This was included in Folsom:

commit 3114a97ba188895daff4a3d337b2c73855d4632d
Author: Daniel P. Berrange <>
Date:   Mon Jun 11 17:16:10 2012 +0100

    Update default policies for KVM guest PIT & RTC timers
    The default policies for the KVM guest PIT and RTC timers
    are not very good at maintaining reliable time in guest
    operating systems. In particular Windows 7 guests will
    often crash with the default KVM timer policies, and old
    Linux guests will have very bad time drift
    Set the PIT such that missed ticks are injected at the
    normal rate, ie they are delayed
    Set the RTC such that missed ticks are injected at a
    higher rate to "catch up"
    This corresponds to the following libvirt XML
      <clock offset='utc'>
        <timer name='pit' tickpolicy='delay'/>
        <timer name='rtc' tickpolicy='catchup'/>
    And the following KVM options
      -rtc base=utc,driftfix=slew
    This should provide a default configuration that works
    acceptably for most OS types. In the future this will
    likely need to be made configurable per-guest OS type.
    Fixes LP bug #1011848
    Change-Id: Iafb0e2192b5f3c05b6395ffdfa14f86a98ce3d1f
    Signed-off-by: Daniel P. Berrange <>

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