Can I change which timer interrupts occur?
On my Debian 8 system, when I run the command watch -n0.1 --no-title cat /proc/interrupts
, I get the output below.
CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 [0/1808]
0: 46 0 0 10215 0 0 0 0 IO-APIC-edge timer
1: 1 0 0 2 0 0 0 0 IO-APIC-edge i8042
8: 0 0 0 1 0 0 0 0 IO-APIC-edge rtc0
9: 0 0 0 0 0 0 0 0 IO-APIC-fasteoi acpi
12: 0 0 0 4 0 0 0 0 IO-APIC-edge i8042
18: 0 0 0 0 8 0 0 0 IO-APIC-fasteoi i801_smbus
19: 7337 0 0 0 0 0 0 0 IO-APIC-fasteoi ata_piix, ata_piix
21: 0 66 0 0 0 0 0 0 IO-APIC-fasteoi ehci_hcd:usb1
23: 0 0 35 0 0 0 0 0 IO-APIC-fasteoi ehci_hcd:usb2
40: 208677 0 0 0 0 0 0 0 HPET_MSI-edge hpet2
41: 0 4501 0 0 0 0 0 0 HPET_MSI-edge hpet3
42: 0 0 2883 0 0 0 0 0 HPET_MSI-edge hpet4
43: 0 0 0 1224 0 0 0 0 HPET_MSI-edge hpet5
44: 0 0 0 0 1029 0 0 0 HPET_MSI-edge hpet6
45: 0 0 0 0 0 0 0 0 PCI-MSI-edge aerdrv, PCIe PME
46: 0 0 0 0 0 0 0 0 PCI-MSI-edge PCIe PME
47: 0 0 0 0 0 0 0 0 PCI-MSI-edge PCIe PME
48: 0 0 0 0 0 0 0 0 PCI-MSI-edge PCIe PME
49: 0 0 0 0 0 8570 0 0 PCI-MSI-edge eth0-rx-0
50: 0 0 0 0 0 0 1684 0 PCI-MSI-edge eth0-tx-0
51: 0 0 0 0 0 0 0 2 PCI-MSI-edge eth0
NMI: 8 2 2 2 1 2 1 49 Non-maskable interrupts
LOC: 36 31 29 26 21 7611 886 1390 Local timer interrupts
SPU: 0 0 0 0 0 0 0 0 Spurious interrupts
PMI: 8 2 2 2 1 2 1 49 Performance monitoring interrupts
IWI: 0 0 0 1 1 0 1 0 IRQ work interrupts
RTR: 7 0 0 0 0 0 0 0 APIC ICR read retries
RES: 473 1027 1530 739 1532 3567 1529 1811 Rescheduling interrupts
CAL: 846 1012 1122 1047 984 1008 1064 1145 Function call interrupts
TLB: 2 7 5 3 12 15 10 6 TLB shootdowns
TRM: 0 0 0 0 0 0 0 0 Thermal event interrupts
THR: 0 0 0 0 0 0 0 0 Threshold APIC interrupts
MCE: 0 0 0 0 0 0 0 0 Machine check exceptions
MCP: 4 4 4 4 4 4 4 4 Machine check polls
THR: 0 0 0 0 0 0 0 0 Hypervisor callback interrupts
ERR: 0
MIS: 0
Note that the timer interrupt fires mostly on CPU3.
Is it possible to move the timer interrupt to CPU0?
source to share
The name of the IRQ SMP affinity concept .
The smp_affinity IRQ can be set by setting the affinity mask to /proc/irq/<IRQ_NUMBER>/smp_affinity
or the affinity list to /proc/irq/<IRQ_NUMBER>/smp_affinity_list
.
An affinity mask is a bit field where each bit represents a kernel, IRQs are allowed to be served on kernels corresponding to the set bits.
Command
echo 1 > /proc/irq/0/smp_affinity
executed as root should bind IRQ0 to CPU0.
The condition is mandatory because setting an IRQ affinity is subject to many prerequisites, the list includes: an interrupt controller that maintains a forwarding table (e.g. IO-APIC ), the affinity mask must contain at least one active CPU, the IRQ affinity must not be managed by the kernel and the function must be enabled.
On my virtualized Debian 8 system, I was unable to set the proximity of IRQ0 without getting an EIO error.
I also couldn't find the exact reason.
If you want to dive into the Linux source code, you can start with write_irq_affinity in proc.c
source to share