User`s guide

Soft lockup errors when booting

When upgrading or installing the UEK R3 kernel on fast hardware, usually with SAN storage attached,

the kernel can fail to boot and BUG: soft lockup messages are displayed in the console log. The

workaround is to increase the baud rate from the default value of 9600 by amending the kernel boot line in

/boot/grub/grub.conf to include an appropriate console setting, for example:

console=ttyS0,115200n8

A value of 115200 is recommended as smaller values such as 19200 are known to be insufficient

for some systems (for example, see http://docs.oracle.com/cd/E19045-01/blade.x6220/820-0048-18/

sp.html#0_pgfId-1002490). If the host implements an integrated system management infrastructure, such

as ILOM on Sun and Oracle systems or iLO on HP systems, configure the integrated console baud rate

to match the setting for the host system. Otherwise, the integrated console is likely to display garbage

characters. (Bug ID 17064059, 17252160)

Transparent Huge Pages

This release removes the Transparent Huge Pages (THP) feature. Following extensive benchmarking

and testing, Oracle found that THP caused a performance degradation of between 5 and 10% for some

workloads. This performance degradation was a result of a slower memory allocator code path being used

even when the applications were not using THP. When the fact that huge pages are not swappable was

taken into account, the positive effect that THP should provide was outweighed by its negative effects.

After installing this UEK release, you cannot enable THP (for example, by specifying kernel boot

parameters). The THP settings under /sys/kernel/mm/transparent_hugepage have also been

removed. A future update might contain an updated THP implementation which resolves the performance

issue.

Note

This change does not affect support for applications that use explicit huge pages

(for example, Oracle Database).

(Bug ID 16823432)

User Namespaces

The kernel functionality (CONFIG_USER_NS) that allows unprivileged processes to create namespaces

for users inside which they have root privileges is not currently implemented because of a clash with the

implementation of XFS. This functionality is primarily intended for use with Linux Containers. As a result,

the lxc-checkconfig command displays User namespace: missing. (Bug ID 16656850)

Virtualization

• When booting UEK R3 as a PVHVM guest, you can safely ignore the following kernel message:

register_vcpu_info failed:

err=-38

(Bug ID 13713774)

• Under Oracle VM Server 3.1.1, migrating a PVHVM guest that is running the UEK R3 kernel causes

a disparity between the date and time as displayed by date and hwclock. The workaround post

migration is either to run the command hwclock --hctosys on the guest or to reboot the guest. (Bug

ID 16861041)