Bug 755426

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.