Bug 705254

Summary:	Time drift on rhel5.7 guest when savevm/loadvm
Product:	Red Hat Enterprise Linux 5	Reporter:	Mike Cao <bcao>
Component:	kvm	Assignee:	Virtualization Maintenance <virt-maint>
Status:	CLOSED WONTFIX	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	5.7	CC:	bcao, gcosta, juzhang, michen, mkenneth, rhod, virt-maint, zamsden
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-07-17 12:48:36 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Bug Depends On:
Bug Blocks:	580949

Description Mike Cao 2011-05-17 07:12:01 UTC

Description of problem:


Version-Release number of selected component (if applicable):
Host info
# uname -r
2.6.18-260.el5
[root@t1 ~]# rpm -q kmv
package kmv is not installed
[root@t1 ~]# rpm -q kvm
kvm-83-232.el5

Guest info:
# uname -r
2.6.18-261.el5

How reproducible:
2/2

Steps to Reproduce:
1.sync host's clock with ntpserver
2.start VM
/usr/libexec/qemu-kvm -M rhel5.6.0 -m 2G -smp 4,sockets=4,cores=1,threads=1 -name VM -uuid 02b8079c-cca0-ae65-c63a-a2aa4119497d -monitor stdio -no-kvm-pit-reinjection -rtc-td-hack -usbdevice tablet -startdate now -boot c -drive file=/home/rhel5_7_64.qcow2,if=virtio,format=qcow2,werror=stop,cache=none,boot=on -net nic,macaddr=54:52:40:33:4c:58,vlan=0,model=virtio -net tap -usb -vnc :1 -k en-us -balloon virtio -notify all -no-hpet
3.check clock drift in the guest 
  ---->Actual Result of this step:no time drift
4.(qemu)savevm  ,after that check clock drift of guest  
  ---->Actual Result of this step: no time drift
5.(qemu)loadvm 1 ,after that check clock drift of guest
  
Actual results:
after step5,
# ntpdate -q clock.redhat.com
server 66.187.233.4, stratum 1, offset 3443.028276, delay 0.31119
17 May 02:04:43 ntpdate[3474]: step time server 66.187.233.4 offset 3443.028276 sec

Expected results:
time drift should less than 5 secs

Additional info:
1.guest use kvm clocksource
2.Tried with clock=tsc in the guest ,hit the same issue.
3.Host use TSC clocksource
4.Not sure whether this one is same as Bug 703335, reported in case of missing bug.

Comment 2 Mike Cao 2011-05-17 09:16:00 UTC

Windows 2003R2sp2 64 bit guest hit the same issue .

Comment 3 Zachary Amsden 2011-05-17 16:11:08 UTC

This absolutely need to be investigated, it's not a RHEL 5.X bug, it's a problem with time keeping in the hypervisor instead - using KVM clock, guest time should stay caught up to real time.

Windows guests and TSC based timekeeping problems are interesting and possibly related, but most definitely not the same bug.  Windows may not immediately catch back up to real time, and TSC based timekeeping may fail for a number of reasons to catch back up the real time.

This should remain open to track why guests using kvm-clock are not catching back up to real time immediately, which is supposed to be the advantage of KVM clock over other clocksources to begin with.

Comment 4 Mike Cao 2011-05-18 06:52:14 UTC

(In reply to comment #2)
> Windows 2003R2sp2 64 bit guest hit the same issue .

in comment #0 step4
for linux guest ,no time drift occurs
for windows guest ,time drift occures 

So windows guest time drift related to guest (qemu)stop instead of (qemu)savevm
more info ,referring to Bug 705686

Comment 5 Zachary Amsden 2011-06-22 01:22:50 UTC

This is almost certainly a dup of 694398, although it may need to be tracked separately to get the fix into a different release.

Comment 7 Ronen Hod 2011-07-17 12:48:36 UTC

There are other time-drift bugs, and this one saveVm+loadvm is not critical, nor it is reported by a customer, so I close it.