6. Tools Updates

SystemTap is now fully supported, and has been re-based to the latest upstream version. This update features improved user-space probing through shared libraries, experimental DWARF unwinding, and a new <sys/sdt.h> header file which provides dtrace-compatible markers.

This re-base also enhances support for debuginfo-less operations. Typecasting (through the @cast operator) is now supported, along with kernel tracepoint probing. Several 'kprobe.*' probe bugs that hampered debuginfo-less operations are also now resolved.

SystemTap also features several documentation improvements. A new '3stap' feature provides users with useful man pages on most SystemTap probes and functions. The systemtap-testsuite package also features a larger library of sample scripts.

For more information about the SystemTap re-base, please refer to the SystemTap section Package Updates chapter of the Technical Notes.

Systemtap tracepoints are placed in important sections of the kernel, allowing system administrators to analyze the performance of, and debug portions of code. In Red Hat Enterprise Linux 5.4, tracepoints have been added to the following sections of the kernel subsystem as a Technology Preview:

The Gnu Compiler Collection version 4.4 (GCC4.4) is now included in this release as a Technology Preview. This collection of compilers include C, C++, and Fortran compilers along with support libraries.

glibc new MALLOC behaviour: The upstream glibc has been changed recently to enable higher scalability across many sockets and cores. This is done by assigning threads their own memory pools and by avoiding locking in some situations. The amount of additional memory used for the memory pools (if any) can be controlled using the environment variables MALLOC_ARENA_TEST and MALLOC_ARENA_MAX.

MALLOC_ARENA_TEST specifies that a test for the number of cores is performed once the number of memory pools reaches this value. MALLOC_ARENA_MAX sets the maximum number of memory pools used, regardless of the number of cores.

The glibc in the RHEL 5.4 release has this functionality integrated as a Technology Preview of the upstream malloc. To enable the per-thread memory pools the environment variable MALLOC_PER_THREAD needs to be set in the environment. This environment variable will become obsolete when this new malloc behaviour becomes default in future releases. Users experiencing contention for the malloc resources could try enabling this option.