Bug 755426 - kvm and preemption model
Summary: kvm and preemption model
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: kernel
Version: 6.1
Hardware: x86_64
OS: Linux
unspecified
high
Target Milestone: rc
: ---
Assignee: Karen Noel
QA Contact: Red Hat Kernel QE team
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2011-11-21 05:46 UTC by livelace
Modified: 2013-01-09 14:03 UTC (History)
1 user (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2012-11-28 12:43:31 UTC
Target Upstream Version:


Attachments (Terms of Use)

Description livelace 2011-11-21 05:46:10 UTC
Description of problem:

When you start the virtual machine, and further work on the host system - slows down in graphics applications. In this case the system load is minimal.
This occurs in approximately equal intervals (slowing down for 5 minutes and 10 minutes of normal operation).

Version-Release number of selected component (if applicable):

1. 2.6.32-131.17.1.el6.x86_64
2. qemu-kvm-0.12.1.2-2.160.el6_1.8.x86_64
3. Virtual machines (linux,windows)
4. Kernel config:

# CONFIG_TREE_PREEMPT_RCU is not set
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

Hardware:

1. Core i7 920
2. 12 Gb DDR3
3. two raid10 sata 3 Gb/s

What has been tested:

1. CPU (create archive)
2. RAM (check for errors)
3. soft raid (180 Mb/s average speed)
4. iostat
5. perf top
6. Disabling the periphery
7. Put kernel parameters acpi=off
8. Disable and remove pulseaudio
9. Full disable selinux
10. Set in cgroup for user:

cpu.shares=10000;
cpu.rt_runtime_us=900000;
cpu.rt_period_us=1000000; 

blkio.weight=1000;

How reproducible:

Run virtual machine and work with graphics applications.

Additional info:

Search in google:

http://lkml.indiana.edu/hypermail/linux/kernel/0707.3/0698.html

Current kvm disables preemption while the new virtualization registers are
in use. This of course is not very good for latency sensitive workloads (one
use of virtualization is to offload user interface and other latency
insensitive stuff to a container, so that it is easier to analyze the
remaining workload). This patch re-enables preemption for kvm; preemption
is now only disabled when switching the registers in and out, and during
the switch to guest mode and back.

Comment 3 RHEL Program Management 2012-05-03 05:28:36 UTC
Since RHEL 6.3 External Beta has begun, and this bug remains
unresolved, it has been rejected as it is not proposed as
exception or blocker.

Red Hat invites you to ask your support representative to
propose this request, if appropriate and relevant, in the
next release of Red Hat Enterprise Linux.

Comment 4 Avi Kivity 2012-05-14 15:02:18 UTC
The link you posted is outdated, it has been merged long ago.  What exactly are you experiencing? Are you sure it isn't just the impact of the extra cpu load?

Comment 6 livelace 2013-01-09 14:03:36 UTC
Using 6.3 on same hardware - all is good. CPU/GPU load is high, but no freeze.


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