I've looked into linux server tuning docs that mention installing irqbalance (http://www.irqbalance.org/) on SMP systems. I'm looking at it now on a quad-core system, and while "ps axf" can tell me it is running, I don't see any stats or information of any sorts on if/how it has affected the system.

Anyone know where to look?

  • I think the page says it all: "To a large degree, the work irqbalance does is invisible to you; if irqbalance performs its job right, nobody will ever notice it's there or want to turn it off." :P – Kamil Kisiel Oct 19 '09 at 22:58

in the sourcecode they reference /proc a few time. Maybe you find your answers there. root@[/usr/local/src/irqbalance-0.55]egrep -ri "proc|sys" *

activate.c:                     sprintf(buf, "/proc/irq/%i/smp_affinity", irq->number);
cpumask.h: * set of CPU's in a system, one bit position per CPU number.
cpumask.h: * The following particular system cpumasks and operations manage
cpumask.h: *  be plugged in at anytime during the life of that system boot.
cpumask.h:int highest_possible_processor_id(void);
cputree.c: * This file contains the code to construct and manipulate a hierarchy of processors,
cputree.c: * cache domains and processor cores.
cputree.c:#include <sys/types.h>
cputree.c:      dir = opendir("/sys/devices/system/cpu");
cputree.c:                      sprintf(new_path, "/sys/devices/system/cpu/%s", entry->d_name);
irqbalance.c:#include <sys/time.h>
irqbalance.c:   /* On single core UP systems irqbalance obviously has no work to do */
irqbalance.c:   /* On dual core/hyperthreading shared cache systems just do a one shot setup */
irqbalance.c:   parse_proc_interrupts();
irqbalance.c:   parse_proc_interrupts();
irqbalance.c:           parse_proc_interrupts();
irqbalance.c:           /* cope with cpu hotplug -- detected during /proc/interrupts parsing */
irqbalance.h:extern void parse_proc_interrupts(void);
irqlist.c:#include <sys/types.h>
irqlist.c: * This function classifies and reads various things from /proc about a specific irq
irqlist.c:      sprintf(buf, "/proc/irq/%i", number);
irqlist.c:                      sprintf(buf, "/proc/irq/%i/smp_affinity", number);
Makefile:LIBS=bitmap.o irqbalance.o cputree.o  procinterrupts.o irqlist.o placement.o activate.o network.o powermode.o numa.o classify.o
network.c:#include <sys/ioctl.h>
network.c:        sprintf(buffer,"/sys/bus/pci/devices/%s/irq", driver.bus_info);
network.c:      file = fopen("/proc/net/dev", "r");
numa.c:#include <sys/types.h>
numa.c: dir = opendir("/sys/bus/pci/devices");
numa.c:         sprintf(line,"/sys/bus/pci/devices/%s/irq", entry->d_name);
numa.c:         sprintf(line,"/sys/bus/pci/devices/%s/class", entry->d_name);
numa.c:         sprintf(line,"/sys/bus/pci/devices/%s/local_cpus", entry->d_name);
numa.c: * Ethernet gets the type via /proc/net/dev; in addition down'd interfaces
powermode.c:    file = fopen("/proc/stat", "r");
powermode.c:    dummy = strtoull(c, &c, 10); /* system */
procinterrupts.c:void parse_proc_interrupts(void)
procinterrupts.c:       file = fopen("/proc/interrupts", "r");

Based on evildeed's answer running sudo cat /proc/irq/*/smp_affinity should tell you. If you get amore then one answer it should be working.

As the output is an integer transform of a bitmask it can be hard to understand for non-programmer types.


  • Bound to cpu0 - 1
  • Bound to cpu1 - 2
  • Bound to cpu0 and/or cpu1 - 3
  • Bound to cpu3,4,7 - 282

You can get a general idea of if it is doing anything by doing cat /proc/interrupts and seeing if the processes that you were trying to isolate are on creating interrupts on the processors that are supposed to be running your high priority process.

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