IBM AIX Continuous Availability Features - IBM Redbooks

The new processor autonomously replaces the defective one. Dynamic CPU Guard and
Dynamic CPU Sparing work together to protect a customer's investments through their
self-diagnosing and self-healing software. More information is available at the following site:
http://www.research.ibm.com/journal/sj/421/jann.html
2.1.4 Predictive CPU deallocation and dynamic processor deallocation
On these systems, AIX implements continuous hardware surveillance and regularly polls the
firmware for hardware errors. When the number of processor errors hits a threshold and the
firmware recognizes that there is a distinct probability that this system component will fail,
then the firmware returns an error report. In all cases, the error is logged in the system error
log. In addition, on multiprocessor systems, depending on the type of failure, AIX attempts to
stop using the untrustworthy processor and deallocate it. More information is available at the
following site:
http://www-05.ibm.com/cz/power6/files/zpravy/WhitePaper_POWER6_availabilty.PDF
2.1.5 Processor recovery and alternate processor
Although this is related mainly to System p hardware, AIX still plays a role in this process and
coding in AIX allows the alternate processor recovery feature to deallocate and deconfigure a
failing processor by moving the instruction stream over to and restarting it on a spare
processor. These operations can be accomplished by the POWER Hypervisor and
POWER6 hardware without application interruption, thus allowing processing to continue
unimpeded. More information is available at the following site:
http://www-05.ibm.com/cz/power6/files/zpravy/WhitePaper_POWER6_availabilty.PDF
2.1.6 Excessive interrupt disablement detection
AIX V5.3 ML3 has introduced a new feature which can detect a period of excessive interrupt
disablement on a CPU, and create an error log record to report it. This allows you to know if
privileged code running on a system is unduly (and silently) impacting performance. It also
helps to identify and improve such offending code paths before the problems manifest in
ways that have proven very difficult to diagnose in the past.
This feature employs a kernel profiling approach to detect disabled code that runs for too
long. The basic idea is to take advantage of the regularly scheduled clock “ticks” that
generally occur every 10 milliseconds, using them to approximately measure continuously
disabled stretches of CPU time individually on each logical processor in the configuration.
This approach will alert you to partially disabled code sequences by logging one or more hits
within the offending code. It will alert you to fully disabled code sequences by logging the
i_enable that terminates them.
You can turn excessive interrupt disablement off and on, respectively, by changing the
proc.disa RAS component:
errctrl -c proc.disa errcheckoff
errctrl -c proc.disa errcheckon
Note that the preceding commands only affect the current boot. In AIX 6.1, the -P flag is
introduced so that the setting can be changed persistently across reboots, for example:
errctrl -c proc.disa -P errcheckoff
Chapter 2. AIX continuous availability features 13