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KVM Cookbook

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Interrupt affinity

In addition to enabling SR-IOV in the VM host, to fully take advantage of SR-IOV performance improvements you must configure interrupt affinity for your FortiGate-VM. Interrupt affinity (also called CPU affinity) maps FortiGate-VM interrupts to the CPUs that are assigned to your FortiGate-VM. You use a CPU affinity mask to define the CPUs that the interrupts are assigned to.

A common use of this feature would be to improve your FortiGate-VM's networking performance by:

  • On the VM host, add multiple host CPUs to your FortiGate-VM.
  • On the VM host, configure CPU affinity to specify the CPUs that the FortiGate-VM can use.
  • On the VM host, configure other VM clients on the VM host to use other CPUs.
  • On the FortiGate-VM, assign network interface interrupts to a CPU affinity mask that includes the CPUs that the FortiGate-VM can use.

In this way, all available CPU interrupts for the configured host CPUs are used to process traffic on your FortiGate interfaces. This configuration could lead to improve FortiGate-VM network performance because you have dedicated VM host CPU cycles to processing your FortiGate-VM's network traffic.

You can use the following CLI command to configure interrupt affinity for your FortiGate-VM:

config system affinity-interrupt

edit <index>

set interrupt <interrupt-name>

set affinity-cpumask <cpu-affinity-mask>

next

end

Where:

  • <interrupt-name> is the name of the interrupt to associate with a CPU affinity mask. You can view your FortiGate-VM interrupts using the diagnose hardware sysinfo interrupts command. Usually you would associate all of the interrupts for a given interface with the same CPU affinity mask.
  • <cpu-affinity-mask> is the CPU affinity mask for the CPUs that will process the associated interrupt.

For example, consider the following configuration:

  • The port2 and port3 interfaces of a FortiGate-VM send and receive most of the traffic.
  • On the VM host you have set up CPU affinity between your FortiGate-VM and four CPUs (CPU 0, 1 , 2, and 3).
  • SR-IOV is enabled and SR-IOV interfaces use the i40evf interface driver.

The output from the diagnose hardware sysinfo interrupts command shows that port2 has the following transmit and receive interrupts:

i40evf-port2-TxRx-0

i40evf-port2-TxRx-1

i40evf-port2-TxRx-2

i40evf-port2-TxRx-3

The output from the diagnose hardware sysinfo interrupts command shows that port3 has the following transmit and receive interrupts:

i40evf-port3-TxRx-0

i40evf-port3-TxRx-1

i40evf-port3-TxRx-2

i40evf-port3-TxRx-3

Use the following command to associate the port2 and port3 interrupts with CPU 0, 1 , 2, and 3.

config system affinity-interrupt

edit 1

set interrupt "i40evf-port2-TxRx-0"

set affinity-cpumask "0x0000000000000001"

next

edit 2

set interrupt "i40evf-port2-TxRx-1"

set affinity-cpumask "0x0000000000000002"

next

edit 3

set interrupt "i40evf-port2-TxRx-2"

set affinity-cpumask "0x0000000000000004"

next

edit 4

set interrupt "i40evf-port2-TxRx-3"

set affinity-cpumask "0x0000000000000008"

next

edit 1

set interrupt "i40evf-port3-TxRx-0"

set affinity-cpumask "0x0000000000000001"

next

edit 2

set interrupt "i40evf-port3-TxRx-1"

set affinity-cpumask "0x0000000000000002"

next

edit 3

set interrupt "i40evf-port3-TxRx-2"

set affinity-cpumask "0x0000000000000004"

next

edit 4

set interrupt "i40evf-port3-TxRx-3"

set affinity-cpumask "0x0000000000000008"

next

end

Resources

Interrupt affinity

In addition to enabling SR-IOV in the VM host, to fully take advantage of SR-IOV performance improvements you must configure interrupt affinity for your FortiGate-VM. Interrupt affinity (also called CPU affinity) maps FortiGate-VM interrupts to the CPUs that are assigned to your FortiGate-VM. You use a CPU affinity mask to define the CPUs that the interrupts are assigned to.

A common use of this feature would be to improve your FortiGate-VM's networking performance by:

  • On the VM host, add multiple host CPUs to your FortiGate-VM.
  • On the VM host, configure CPU affinity to specify the CPUs that the FortiGate-VM can use.
  • On the VM host, configure other VM clients on the VM host to use other CPUs.
  • On the FortiGate-VM, assign network interface interrupts to a CPU affinity mask that includes the CPUs that the FortiGate-VM can use.

In this way, all available CPU interrupts for the configured host CPUs are used to process traffic on your FortiGate interfaces. This configuration could lead to improve FortiGate-VM network performance because you have dedicated VM host CPU cycles to processing your FortiGate-VM's network traffic.

You can use the following CLI command to configure interrupt affinity for your FortiGate-VM:

config system affinity-interrupt

edit <index>

set interrupt <interrupt-name>

set affinity-cpumask <cpu-affinity-mask>

next

end

Where:

  • <interrupt-name> is the name of the interrupt to associate with a CPU affinity mask. You can view your FortiGate-VM interrupts using the diagnose hardware sysinfo interrupts command. Usually you would associate all of the interrupts for a given interface with the same CPU affinity mask.
  • <cpu-affinity-mask> is the CPU affinity mask for the CPUs that will process the associated interrupt.

For example, consider the following configuration:

  • The port2 and port3 interfaces of a FortiGate-VM send and receive most of the traffic.
  • On the VM host you have set up CPU affinity between your FortiGate-VM and four CPUs (CPU 0, 1 , 2, and 3).
  • SR-IOV is enabled and SR-IOV interfaces use the i40evf interface driver.

The output from the diagnose hardware sysinfo interrupts command shows that port2 has the following transmit and receive interrupts:

i40evf-port2-TxRx-0

i40evf-port2-TxRx-1

i40evf-port2-TxRx-2

i40evf-port2-TxRx-3

The output from the diagnose hardware sysinfo interrupts command shows that port3 has the following transmit and receive interrupts:

i40evf-port3-TxRx-0

i40evf-port3-TxRx-1

i40evf-port3-TxRx-2

i40evf-port3-TxRx-3

Use the following command to associate the port2 and port3 interrupts with CPU 0, 1 , 2, and 3.

config system affinity-interrupt

edit 1

set interrupt "i40evf-port2-TxRx-0"

set affinity-cpumask "0x0000000000000001"

next

edit 2

set interrupt "i40evf-port2-TxRx-1"

set affinity-cpumask "0x0000000000000002"

next

edit 3

set interrupt "i40evf-port2-TxRx-2"

set affinity-cpumask "0x0000000000000004"

next

edit 4

set interrupt "i40evf-port2-TxRx-3"

set affinity-cpumask "0x0000000000000008"

next

edit 1

set interrupt "i40evf-port3-TxRx-0"

set affinity-cpumask "0x0000000000000001"

next

edit 2

set interrupt "i40evf-port3-TxRx-1"

set affinity-cpumask "0x0000000000000002"

next

edit 3

set interrupt "i40evf-port3-TxRx-2"

set affinity-cpumask "0x0000000000000004"

next

edit 4

set interrupt "i40evf-port3-TxRx-3"

set affinity-cpumask "0x0000000000000008"

next

end