Installation guide

# 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 cop-
ies 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 follow-
ing 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 ac-
counting 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 in-
form the tool vendor (for malfunctioning third-party tools).
7. Kernel-Related Information
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