Distribution of VME Interrupts on Multiprocessors

Distribution of VME Interrupts on Multiprocessors

On CHALLENGE/Onyx, POWER CHALLENGE/POWER Onyx, and multiprocessor POWER Series systems, VME interrupt levels can be individually locked onto any processor in the system through the IPL directive. This prevents a processor running a real-time process or a process that needs a guaranteed response from being interrupted inconveniently, and it makes system load balancing easier. To lock a particular VME interrupt level to a processor, edit the /var/sysgen/system/irix.sm file, then run lboot to implement the changes. The format is:

IPL: level cpu#

where level is the priority level (1-7, with 7 being the highest), and cpu# is the number of the CPU on which you want the VME interrupts of that level to occur. For example:

IPL: 4 1

designates VME interrupt priority level 4 on CPU number 1.

CHALLENGE/Onyx and POWER CHALLENGE/POWER Onyx and multiprocessor POWER Series(TM) systems take advantage of multiple CPUs by distributing interrupts across all processors. These distributed interrupts are called sprayed interrupts. To declare a CPU that is not suitable for sprayed interrupts (usually because they will be used for real-time activities), use the NOINTR directive.

Example: to declare that CPU 3 will not accept sprayed interrupts, use:

NOINTR: 3

You can tie a VME interrupt to a processor that accepts no sprayed interrupts using the IPL directives described above. You may not restrict CPU 0 from receiving interrupts. You can specify multiple CPUs on the NOINTR line.

After editing the irix.sm file, you must run lboot to reconfigure the system before the changes can take effect. autoconfig is a script in /etc/init.d that runs lboot. See the autoconfig(1M), lboot(1M), and system(4) man pages for details.