Bug 606981

Summary:	qemu-kvm using CPU when vm is paused
Product:	Red Hat Enterprise Linux 6	Reporter:	Roland McGrath <roland>
Component:	qemu-kvm	Assignee:	Virtualization Maintenance <virt-maint>
Status:	CLOSED NOTABUG	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	medium	Docs Contact:
Priority:	low
Version:	6.1	CC:	agrover, amit.shah, berrange, dwmw2, ehabkost, gcosta, itamar, jaswinder, jforbes, juzhang, knoel, markmc, mkenneth, ondrejj, scottt.tw, tburke, virt-maint, virt-maint
Target Milestone:	rc	Keywords:	Reopened
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-07-07 14:03:05 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Roland McGrath 2010-06-22 20:34:31 UTC

Description of problem:
A paused qemu-kvm VM uses CPU time, in small amounts, but steadily without end.

Version-Release number of selected component (if applicable):
qemu-system-x86-0.12.3-8.fc13.x86_64
kernel-2.6.33.5-124.fc13.x86_64 (host and guest both)

How reproducible:
100%

Steps to Reproduce:
1.virt-manager new x86_64 vm with install of Fedora 13
2.complete install, update, reboot vm, leave at gdm login prompt for some minutes
3.hit pause button in virt-manager
4.run top on host, see qemu-kvm using some CPU steadily (1-5% CPU on my box)
  
Actual results:
paused vm consumes CPU

Expected results:
paused vm consumes no CPU

Additional info:

I also see ksmd often using a bunch of CPU intermittently.  However, if I "service ksm stop", then ksmd goes away and qemu-kvm still uses CPU.

Comment 1 Bug Zapper 2011-06-01 15:52:16 UTC

This message is a reminder that Fedora 13 is nearing its end of life.
Approximately 30 (thirty) days from now Fedora will stop maintaining
and issuing updates for Fedora 13.  It is Fedora's policy to close all
bug reports from releases that are no longer maintained.  At that time
this bug will be closed as WONTFIX if it remains open with a Fedora 
'version' of '13'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version prior to Fedora 13's end of life.

Bug Reporter: Thank you for reporting this issue and we are sorry that 
we may not be able to fix it before Fedora 13 is end of life.  If you 
would still like to see this bug fixed and are able to reproduce it 
against a later version of Fedora please change the 'version' of this 
bug to the applicable version.  If you are unable to change the version, 
please add a comment here and someone will do it for you.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events.  Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

The process we are following is described here: 
http://fedoraproject.org/wiki/BugZappers/HouseKeeping

Comment 2 Bug Zapper 2011-06-27 18:46:04 UTC

Fedora 13 changed to end-of-life (EOL) status on 2011-06-25. Fedora 13 is 
no longer maintained, which means that it will not receive any further 
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of 
Fedora please feel free to reopen this bug against that version.

Thank you for reporting this bug and we are sorry it could not be fixed.

Comment 3 Andy Grover 2011-06-27 20:54:42 UTC

I'm seeing this issue with RHEL 6.1 as well.

Comment 5 Dor Laor 2011-07-07 14:03:05 UTC

The guest vcpus are paused. qemu-kvm has other threads running (like vncserve, monitor and some kernel threads (timer) that keeps on ticking. In theory it is possible to pause them too but I don't see the value.