Architecture Specific Support; I386 - Red Hat ENTERPRISE LINUX 5.4 - RELEASE NOTES Release Note

Release Notes
• 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.

7. Architecture Specific Support

7.1. i386

• In a virtual environment, timekeeping for Red Hat Enterprise Linux 64-bit kernels can be
problematic, since time is kept by counting timer interrupts. De- and re-scheduling the virtual
machine can cause a delay in these interrupts, resulting in a timekeeping discrepancy. This kernel
release reconfigures the timekeeping algorithm to keep time based on a time-elapsed counter.
23
(Bugzilla #463573
)
• It was found that, if their stacks exceed the combined size of ~4GB, 64-bit threaded applications
slowed down drastically in pthread_create(). This is because glibc uses MAP_32BIT to
allocate those stacks. As the use of MAP_32BIT is a legacy implementation, this update adds a new
flag (MAP_STACK mmap) to the kernel to avoid constraining 64-bit applications.
• The update includes a feature bit that encourages TSCs to keep running in deep-C states. This bit
NONSTOP_TSC acts in conjunction with CONSTANT_TSC. CONSTANT_TSC indicates that the TSC
runs at constant frequency irrespective of P/T- states, and NONSTOP_TSC indicates that TSC does
not stop in deep C-states.
• This update includes a patch to include asm-x86_64 headers in kernel-devel packages built on or
for i386, i486, i586 and i686 architectures.
• This update includes a fix to ensure that specifying memmap=X$Y as a boot parameter on i386
architectures yields a new BIOS map.
• This update adds a patch to correct a problem with the Non-Maskable Interrupt (NMI) that appeared
in previous kernel releases. The problem appeared to affect various Intel processors and caused the
system to report the NMI watchdog was 'stuck'. New parameters in the NMI code correct this issue.
28
(Bugzilla #500892
)
• This release re-introduces PCI Domain support for HP xw9400 and xw9300 systems.
29
#474891
)
• Functionality has been corrected to export module powernow-k8 parameters to /sys/modules. This
information was previously not
8
25
(Bugzilla #474091
)
(Bugzilla #491775
(Bugzilla #464500
exported.(Bugzilla #492010
26
)
27
)
30
)
24
(Bugzilla #459321
)
(Bugzilla