Red Hat Enterprise Linux Installation Guide 5.2 - linux.meuhobby.com

Chapter 22. Additional Information for IBM System z Users
# ifup ethn
# ifup trn
7. Kernel-Related Information
Red Hat Enterprise Linux includes a modification to the way the Linux kernel timer interrupt is
handled. Normally, a hardware timer is set to generate periodic interrupts at a fixed rate (100
times a second for most architectures). These periodic timer interrupts are used by the kernel to
schedule various internal housekeeping tasks, such as process scheduling, accounting, and
maintaining system uptime.
While a timer-based approach works well for a system environment where only one copy of the
kernel is running, it can cause additional overhead when many copies of the kernel are running
on a single system (for example, as z/VM(R) guests). In these cases, having thousands of
copies of the kernel each generating interrupts many times a second can result in excessive
system overhead.
Therefore, Red Hat Enterprise Linux now includes the ability to turn off periodic timer interrupts.
This is done through the /proc/ file system. To disable periodic timer interrupts, issue the
following command:
echo 0 > /proc/sys/kernel/hz_timer
To enable periodic timer interrupts, issue the following command:
echo 1 > /proc/sys/kernel/hz_timer
By default, periodic timer interrupts are disabled.
Periodic timer interrupt states can also be set at boot-time; to do so, add the following line to
/etc/sysctl.conf to disable periodic timer interrupts:
kernel.hz_timer = 0
Note
Disabling periodic timer interrupts can violate basic assumptions in system
accounting tools. If you notice a malfunction related to system accounting, verify
that the malfunction disappears if periodic timer interrupts are enabled, then
submit a bug at http://bugzilla.redhat.com/bugzilla/ (for malfunctioning bundled
tools), or inform the tool vendor (for malfunctioning third-party tools).
244