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irqbalance - Unix, Linux Command


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NAME

irqbalance - distribute hardware interrupts across processors on a multiprocessor system

SYNOPSIS

irqbalance

DESCRIPTION

The purpose of irqbalance is distribute hardware interrupts across processors on a multiprocessor system in order to increase performance.

OPTIONS

TagDescription
--oneshot
  Causes irqbalance to be run once, after which the daemon exits

--debug Causes irqbalance to run in the foreground and extra debug information to be printed

ENVIRONMENT VARIABLES

TagDescription
IRQBALANCE_ONESHOT
  Same as --oneshot

IRQBALANCE_DEBUG
  Same as --debug

IRQBALANCE_BANNED_CPUS
  Provides a mask of cpus which irqbalance should ignore and never assign interrupts to. This is a hex mask without the leading ’0x’, on systems with large numbers of processors each group of eight hex digits is sepearated ba a comma ’,’. i.e. ‘export IRQBALANCE_BANNED_CPUS=fc0‘ would prevent irqbalance from assigning irqs to the 7th-12th cpus (cpu6-cpu11) or ‘export IRQBALANCE_BANNED_CPUS=ff000000,00000001‘ would prevent irqbalance from assigning irqs to the 1st (cpu0) and 57th-64th cpus (cpu56-cpu63).

IRQBALANCE_BANNED_INTERRUPTS
  Space seperated list of integer irq’s which irqbalance should ignore and never change the affinity of. i.e. export IRQBALANCE_BANNED_INTERRUPTS="205 217 225"

NOTES

The purpose of irqbalance is to distribute interrupts accross cpus in an smp system such that cache-domain affinity is maximized for each irq. In other words, irqbalance tries to assign irqs to cpu cores such that each irq stands a greater chance of having its interrupt handler be in cache when the irq is asserted to the cpu. This raises a few interesting cases in which the behavior of irqbalance may be non-intuitive. Most notably, cases in which a system has only one cache domain. Nominally these systems are only single cpu environments, but can also be found in multi-core environments in which the cores share an L2 cache. In these situations irqbalance will exit immediately, since there is no work that irqbalance can do which will improve interrupt handling performance. This is normal and not cause for concern. For more information regarding irqbalance, please visit http://irqbalance.org/

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