Configuring Xen Processor Affinities; Modifying The Xen Hypervisor - Red Hat ENTERPRISE LINUX 5 - VIRTUALIZATION GUIDE Manual

Chapter 31. Tips and tricks
This rate entry would limit the virtual machine's interface to 10MB/s for outgoing traffic

31.12. Configuring Xen processor affinities

Xen can allocate virtual CPUs to associate with one or more host CPUs. This allocates real processing
resources to virtualized guests. This approach allows Red Hat Enterprise Linux optimize processor
resources when employing dual-core, hyper-threading, or other CPU concurrency technologies. The
Xen credit scheduler automatically balances virtual CPUs between physical ones, to maximize system
use. Red Hat Enterprise Linux allows the credit scheduler to move CPUs around as necessary, as
long as the virtual CPU is pinned to a physical CPU.
If you are running I/O intensive tasks, it is recommended to dedicate either a hyperthread or an entire
processor core to run domain0.
Note that this is unnecessary for KVM as KVM uses the default Linux kernel scheduler.
CPU affinities can be set with virsh or virt-manager:
To set CPU affinities using virsh refer to
To configure and view CPU information with virt-manager refer to
CPUs "
for more information.

31.13. Modifying the Xen hypervisor

Managing host systems often involves changing the boot configuration file /boot/grub/grub.conf.
Managing several or more hosts configuration files quickly becomes difficult. System administrators
often prefer to use the 'cut and paste' method for editing multiple grub.conf files. If you do this,
ensure you include all five lines in the Virtualization entry (or this will create system errors). Hypervisor
specific values are all found on the 'xen' line. This example represents a correct grub.conf
virtualization entry:
# boot=/dev/sda/
default=0
timeout=15
#splashimage=(hd0, 0)/grub/splash.xpm.gz
hiddenmenu
serial ---unit=0 ---speed=115200 ---word=8 ---parity=no ---stop=1
terminal ---timeout=10 serial console
title Red Hat Enterprise Linux Server (2.6.17-1.2519.4.21. el5xen)
root (hd0, 0)
kernel -/xen.gz-2.6.17-1.2519.4.21.el5 com1=115200,8n1
module -/vmlinuz-2.6.17-1.2519.4.21el5xen ro root=/dev/VolGroup00/LogVol00
module -/initrd-2.6.17-1.2519.4.21.el5xen.img
For example, to change the memory entry on your hypervisor (dom0) to 256MB at boot time, edit the
'xen' line and append it with this entry: 'dom0_mem=256M'. This example is the grub.conf with the
hypervisor's memory entry modified.
# boot=/dev/sda
default=0
timeout=15
#splashimage=(hd0,0)/grubs/splash.xpm.gz
hiddenmenu
338
Configuring virtual CPU affinity
for more information.
Section 25.11, "Displaying virtual