Bug 1291252

Summary: [doc] Documentation needed for how a VM syncs time with a Hypervisor
Product: Red Hat Enterprise Linux 7 Reporter: Laura Novich <lnovich>
Component: doc-Virtualization_Deployment_and_Administration_GuideAssignee: Jiri Herrmann <jherrman>
Status: CLOSED CURRENTRELEASE QA Contact:
Severity: unspecified Docs Contact:
Priority: high    
Version: 7.2CC: adevolder, anande, byount, jherrman, jhradile, mtosatti, rhel-docs
Target Milestone: rcKeywords: Documentation
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2016-11-08 17:18:59 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Laura Novich 2015-12-14 12:38:20 UTC 
Description of problem:
Requested by email on the virt-docs list from Anand Nande <anande>, customer support:

On 12/14/2015 05:02 PM, Anand Nande wrote:
> Hi,
>
> It would be great to have a brief article/doc in RHEL-7.x that 
> explains $subject along-with
> * timeline of events when the hypervisor and guest clock change 
> (time-drift)
> * how can they be adjusted back? OR how are they currently adjusted 
> using RH recommended best-practices
>
> Something on the lines of :
>
> more like
>
> host-NTP -> host-date -> host-hwclock
>         |            `-> guest-hwclock -> guest-date (boot)
>         `~> boot_ns [?] -> guest-kvmclock ~> guest-date (runtime)
>
>
> I have not seen this state diagram defined anywhere in our docs or 
> upstream.
> We can take help of Marcelo Tosatti [mtosatti] in this.
>
> Regards
> --Anand




Document URL: 

Section Number and Name: 

Describe the issue: 

Suggestions for improvement: 

Additional information:
Comment 1 Laura Novich 2015-12-14 12:39:54 UTC 
consider making this a standalone article as well.
Comment 3 Laura Novich 2015-12-15 08:55:47 UTC 
Incorporating email from Anand Nande
====================

Something like : http://www.ovirt.org/images/3/3e/StorageLiveMigrationAPIDiagram3.png would be a great idea.

Also we will need to consider the state diagram when the following conditions occur:

    Timer Drift

    Rounding Errors

    Suspend / Resume

    Migration


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