Installation guide

Error Reporting
25
12.3. Error Reporting
12.3.1. Advanced Error Reporting (AER)
The kernel in Red Hat Enterprise Linux 6 features Advanced Error Reporting (AER). AER is a new
kernel feature that provides enhanced error reporting for PCI-Express devices.
12.3.2. Kdump Auto Enablement
Kdump is now enabled by default on systems with large amounts of memory. Specifically, kdump is
enabled by default on:
• systems with more than 4GB of memory on architectures with a 4KB page size (i.e. x86 or x86_64),
or
• systems with more than 8GB of memory on architectures with larger than a 4KB page size (i.e
PPC64).
Note
On systems with less than the above memory configurations, kdump is not auto enabled. Refer
to /usr/share/doc/kexec-tools-2.0.0/kexec-kdump-howto.txt for instructions on
enabling kdump on these systems.
12.4. Power Management
12.4.1. Aggressive Link Power Management (ALPM)
The kernel in Red Hat Enterprise Linux 6 features support for Aggressive Link Power Management
(ALPM). ALPM is a power-saving technique that helps the disk save power by setting a SATA link to
the disk to a low-power setting during idle time (i.e. when there is no I/O). ALPM automatically sets the
SATA link back to an active power state once I/O requests are queued to that link.
12.4.2. Tickless Kernel
Previously the kernel implemented a timer that periodically queried the system to check if there were
any outstanding tasks to process. Consequently, the CPU would remain in an active state, consuming
unnecessary power. The kernel in Red Hat Enterprise Linux 6 enables the new tickless kernel feature,
replacing the periodic timer interrupts with on-demand interrupts. The tickless kernel allows a CPU to
enter longer sleep states when idle, and wake only when a task is queued for processing.
12.5. Analyzing Kernel Performance
12.5.1. Performance Counter for Linux (PCL)
The Linux Performance Counter infrastructure provides an abstraction of performance counter
hardware capabilities, such as instructions executed, cache misses, and branches mis-predicted.
PCL provides per-task and per-CPU counters, and adds event capabilities on top of these counters.
Performance counter information can be used to profile kernel functions and events, and assist in the
analysis of kernel performance issues.