Chapter 44. Kernel

Red Hat Enterprise Linux 7.6 introduces the Extended Berkeley Packet Filter tool (eBPF) as a Technology Preview. This tool is enabled only for the tracing subsystem. For details, see the Red Hat Knowledgebase article at https://access.redhat.com/articles/3550581. (BZ#1559615, BZ#1559756, BZ#1311586)

Red Hat Enterprise Linux 7.3 introduced the heterogeneous memory management (HMM) feature as a Technology Preview. This feature has been added to the kernel as a helper layer for devices that want to mirror a process address space into their own memory management unit (MMU). Thus a non-CPU device processor is able to read system memory using the unified system address space. To enable this feature, add experimental_hmm=enable to the kernel command line. (BZ#1230959)

Red Hat Enterprise Linux 7.2 introduced the criu tool as a Technology Preview. This tool implements Checkpoint/Restore in User-space (CRIU), which can be used to freeze a running application and store it as a collection of files. Later, the application can be restored from its frozen state.

Note that the criu tool depends on Protocol Buffers, a language-neutral, platform-neutral extensible mechanism for serializing structured data. The protobuf and protobuf-c packages, which provide this dependency, were also introduced in Red Hat Enterprise Linux 7.2 as a Technology Preview.

In Red Hat Enterprise Linux 7.6, the criu packages have been upgraded to upstream version 3.9, which provides a number of bug fixes and optimization for the runC container runtime. In addition, support for the 64-bit ARM architectures and the little-endian variant of IBM Power Systems CPU architectures has been fixed. (BZ#1400230, BZ#1464596)

The kexec system call has been provided as a Technology Preview. This system call enables loading and booting into another kernel from the currently running kernel, thus performing the function of the boot loader from within the kernel. Hardware initialization, which is normally done during a standard system boot, is not performed during a kexec boot, which significantly reduces the time required for a reboot. (BZ#1460849)

The kexec fast reboot feature, which was introduced in Red Hat Enterprise Linux 7.5, continues to be available as a Technology Preview. kexec fast reboot makes the reboot significantly faster. To use this feature, you must load the kexec kernel manually, and then reboot the operating system. It is not possible to make kexec fast reboot as the default reboot action. Special case is using kexec fast reboot for Anaconda. It still does not enable to make kexec fast reboot default. However, when used with Anaconda, the operating system can automatically use kexec fast reboot after the installation is complete in case that user boots kernel with the anaconda option. To schedule a kexec reboot, use the inst.kexec command on the kernel command line, or include a reboot --kexec line in the Kickstart file. (BZ#1464377)

The Intel Cache Allocation Technology (CAT) was introduced in Red Hat Enterprise Linux 7.4 as a Technology Preview. However, the perf cqm tool did not work correctly due to an incompatibility between perf infrastructure and Cache Quality of Service Monitoring (CQM) hardware support. Consequently, multiple problems occurred when using perf cqm.

These problems included most notably:

In Red Hat Enterprise Linux 7.5, perf cqm was replaced by the approach based on the resctrl file system, which addressed all of the aforementioned problems. (BZ#1457533, BZ#1288964)

Starting with Red Hat Enterprise Linux 7.6, Traffic Control (TC) Hardware offloading has been provided as a Technology Preview.

Hardware offloading enables that the selected functions of network traffic processing, such as shaping, scheduling, policing and dropping, are executed directly in the hardware instead of waiting for software processing, which improves the performance. (BZ#1503123)

Starting with Red Hat Enterprise Linux 7.6, the AMD xgbe network driver has been provided as a Technology Preview. (BZ#1589397)