Red Hat Enterprise Linux 5 Administration Unleashed

Enabling NMI Watchdog for Locked Systems 447TABLE 21.5Continued-v Display verbose output in four columns instead of three. The fourcolumns, in the order in which they appear, are the RAM addressof the kernel function, the name of the C function in the kernelwhere the clock ticks occurred, the number of clock ticks, and thenormalized load of the procedure as a ratio of the number ofticks to the procedure length.-p Use instead of the default /proc/profile buffer file. Forexample, the kernel profile at a specific point in time can besaved by copying /proc/profile to a different file. Then, thedata can be analyzed later.-V Output the version of readprofile.21The output can be further customized by piping the results through shell utilities such assort, head, tail, grep, and less. For example, to sort the output by the number of clockticks, list the highest numbers first:readprofile -m /boot/System-map-`uname -r` | sort -nrOr, to search for a specific function name:readprofile -m /boot/System-map-`uname -r` | grep Profiling with SystemTapRecently, kprobes, or kernel dynamic probes, have been added to the kernel. These probesallow you to add probes into the kernel for system diagnostics as a kernel module insteadof having to modify the kernel source code before recompiling the kernel.Since then, a project called SystemTap has been started to create a command-line interfaceand scripting language for kprobes, making it easier to use.CAUTIONSystemTap is still in development and rapidly changing. It may not be available on allarchitectures. This section discusses how to get started and how to find the latestinformation on it. SystemTap is not ready for production systems and is subject tochange during its development.To use SystemTap, you need to install the following packages: systemtap, kernel-debuginfo,and kernel-devel. Refer to Chapter 3 for details on installing additional software.The debuginfo packages are not available from RHN. They can be downloaded via FTPfrom the ftp.redhat.com FTP server. After logging in as an anonymous user, change intothe pub/redhat/linux/enterprise//en/os//Debuginfo/ directory,replacing and with the appropriate values for your system. You can alsoview the list of packages by visiting http://ftp.redhat.com/ in a web browser, but it isrecommended that you use an FTP client to download the files.