I've moved a server from one mainboard to another due a disk controller failure.
Since then I've noticed that constantly a 25% of one of the cores goes always to IRQ however I haven't managed myself to know which is the IRQ responsible for that.
The kernel is a Linux 2.6.18-194.3.1.el5 (CentOS). mpstat -P ALL
shows:
18:20:33 CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
18:20:33 all 0,23 0,00 0,08 0,11 6,41 0,02 0,00 93,16 2149,29
18:20:33 0 0,25 0,00 0,12 0,07 0,01 0,05 0,00 99,49 127,08
18:20:33 1 0,14 0,00 0,03 0,04 0,00 0,00 0,00 99,78 0,00
18:20:33 2 0,23 0,00 0,02 0,03 0,00 0,00 0,00 99,72 0,02
18:20:33 3 0,28 0,00 0,15 0,28 25,63 0,03 0,00 73,64 2022,19
This is the /proc/interrupts
cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
0: 245 0 0 7134094 IO-APIC-edge timer
8: 0 0 49 0 IO-APIC-edge rtc
9: 0 0 0 0 IO-APIC-level acpi
66: 67 0 0 0 IO-APIC-level ehci_hcd:usb2
74: 902214 0 0 0 PCI-MSI eth0
169: 0 0 79 0 IO-APIC-level ehci_hcd:usb1
177: 0 0 0 7170885 IO-APIC-level ata_piix, b4xxp
185: 0 0 0 59375 IO-APIC-level ata_piix
NMI: 0 0 0 0
LOC: 7104234 7104239 7104243 7104218
ERR: 0
MIS: 0
How can I identify which IRQ is causing the high CPU usage?
Edit:
Output from dmesg | grep -i b4xxp
wcb4xxp 0000:30:00.0: probe called for b4xx...
wcb4xxp 0000:30:00.0: Identified Wildcard B410P (controller rev 1) at 00012000, IRQ 177
wcb4xxp 0000:30:00.0: VPM 0/1 init: chip ver 33
wcb4xxp 0000:30:00.0: VPM 1/1 init: chip ver 33
wcb4xxp 0000:30:00.0: Hardware echo cancellation enabled.
wcb4xxp 0000:30:00.0: Port 1: TE mode
wcb4xxp 0000:30:00.0: Port 2: TE mode
wcb4xxp 0000:30:00.0: Port 3: TE mode
wcb4xxp 0000:30:00.0: Port 4: TE mode
wcb4xxp 0000:30:00.0: Did not do the highestorder stuff
wcb4xxp 0000:30:00.0: new card sync source: port 3
Best Answer
Well, since you're specifically asking how to know which IRQ is responsible for the number in
mpstat
, you can assume it's not the local interrupt timer (LOC), since those numbers are fairly equal, and yetmpstat
shows some of those cpus at 0 %irq.That leaves IRQ 0, which is the system timer, and which you can't do anything about, and IRQ 177, which is tied to your b4xxp driver.
My guess is that IRQ 177 would be your culprit.
If this is causing a problem, and you would like to change the behavior your see, try:
disabling the software that uses that card, and see if the interrupts decrease.
removing that card from the system, and unloading the driver, and see if there's improvement.
move that card to another slot and see if that helps.
check for updated drivers or patches for the software.
If it's not a problem, and you were just curious, then carry on. :)