VNF Tuning for Performance

This topic provides VNF tuning guidance for VM-Series deployments. It is a reference to help you choose some of the parameter settings for a VM-Series deployment. Before attempting tuning, you should be familiar with the steps to install the VM-Series firewall on the VMware vSphere hypervisor (ESXi), including how to configure tuning parameters and attributes.
This guidance might not apply to VM-Series deployments on top of white-box or grey-box environments targeting SD-WAN, MSSP, or CSSP use-cases.
VM-Series is a high-performance appliance and is available in various form-factors depending on size, hypervisor footprint, and its deployment location in either private or public cloud.
Global and host-level configuration changes impact other VMs running on the same host. You should consider any trade-offs and prudently choose the parameters that best suit your deployment.

ESXi Tuning Parameters

To achieve best results in performance on VM-series, you can tune hardware, hypervisor, and network I/O parameters.
The parameters mentioned here do not apply to every deployment model.

BIOS Settings

This section recommends BIOS Power Management, Hyperthreading, and Intel VT-D settings that can enhance VM-Series firewall performance, and concludes with a sample BIOS configuration.

Power Management

For latency-sensitive applications, any form of power management adds latency to the path where an idle system (in one of several power-saving modes) responds to an external event. VMware recommends setting the BIOS power management setting to “static high performance” (no OS-controlled power management), effectively disabling any form of active power management. Servers with Intel Nehalem class and later CPUs (Intel Xeon 55xx and later) offer two other power management options: C-states and Intel Turbo Boost.
Leaving C-states enabled can increase memory latency and is therefore not recommended for low-latency workloads. Even the enhanced C-state, known as C1E, introduces longer latencies to wake up the CPUs from halt (idle) states to full-power. VMware recommends disabling C1E in the BIOS to further lower latencies.
  • For HP, set Power Regulator Mode to Static High Mode and disable QPI Processor, C-state support, and C1E Support.
  • For Dell, set Power Management Mode, CPU power, and Performance Management to Maximum Performance.
Another parameter to consider is P-states. For outright performance considerations, disable P-state settings on BIOS.
Intel Turbo Boost can lead to performance variations over a period of time. For consistent and deterministic performance, disable Turbo Boost.


If the hardware and BIOS support hyperthreading, ESXi automatically enables hyperthreading on hosts. For the best performance from VM series firewalls, disable hyperthreading on ESXi hosts.
If the deployment environment warrants enabling hyperthreading, then ensure that all CPU resources for the VM-Series firewall are reserved from the same NUMA/Socket node that has access to the PCI devices.
In general, configure the PA-VM as a single NUMA VM. See NUMA and Resource Considerations for more details.

Intel Virtualization Technology for Directed I/O

Intel Virtualization Technology for Directed I/O (Intel VT-D) allows a LAN card to be dedicated to a guest system, which enables increased network performance beyond that of an emulated LAN card. Enable this feature at the BIOS. If you plan to leverage SR-IOV for performance (recommended), enable the SRI-OV BIOS setting.

Sample BIOS Configuration

The following screenshots show the system profile settings and the processor settings for a Dell BIOS.

Physical Settings

Most 1GbE or 10GbE network interface cards (NICs) support a feature called interrupt moderation or interrupt throttling, which coalesces interrupts from the NIC to the host so that the host doesn’t get overwhelmed and spend all its CPU cycles processing interrupts. However, for latency-sensitive workloads, the time the NIC is delaying the delivery of an interrupt for a received packet or a packet that has successfully been sent on the wire is the time that increases the latency of the workload. For best performance on PA-VM, disable interrupt moderation. For example, disable physical NIC interrupt moderation on the ESXi host as follows:
# esxcli system module parameters set -m ixgbe -p "InterruptThrottleRate=0"

Transmit Queue

The ESXi uplink pNIC layer also maintains a software Tx queue of packets queued for transmission, which by default holds 500 packets. If the workload is I/O intensive with large bursts of transmit packets, this queue can overflow, leading to packets being dropped in the uplink layer. The Tx queue size can be increased up to 10,000 packets with the following ESXi command:
# esxcli system settings advanced set -i 10000 -o /Net/MaxNetifTxQueueLen
Depending on the physical NIC and the specific version of the ESXi driver being used on the ESXi host, sometimes packets can be dropped in the pNIC driver because the transmit ring on the pNIC is too small and is filled up. Most pNIC drivers allow you to increase the size of the transmit ring using the following command:
# ethtool -G vmnic0 tx 4096
This command increases the Tx ring size to 4096 entries. The maximum size you can set for a specific pNIC driver, as well as the current Tx ring size in effect, can be determined using the following command:
# ethtool -g vmnic0
Ring parameters for vmnic0: Pre-set maximums: RX: 4096 RX Mini: 0 RX Jumbo: 0 TX: 4096 Current hardware settings: RX: 512 RX Mini: 0 RX Jumbo: 0 TX: 4096

Queue Pairing

Some pNIC drivers, such as Intel’s ixgbe and Broadcom’s bnx2x, also support “queue pairing”, which indicates to the ESXi uplink layer that the receive thread (NetPoll) will also process completion of transmitted packets on a paired transmit queue. For certain transmit-heavy workloads, this can cause delays in processing transmit completions, causing the transmit ring for the vNIC to run out of room for transmitting additional packets, and forcing the vNIC driver in the guest OS to drop packets.
Disabling queue pairing for all pNICs on an ESXi host creates a separate thread for processing pNIC transmit completions. As a result, completions are processed in a timely manner, freeing space in the vNIC’s transmit ring to transmit additional packets.
The ESXi command to disable queue pairing is:
# esxcli system settings advanced set -o /Net/NetNetqRxQueueFeatPairEnable
-i 0
For this to take effect, you must reboot the ESXi host.
If PCI-pass through on VM-700 is used on a dedicated host, no performance tuning of the NIC/NIC driver is needed. However, this deployment mode is not common.

Virtual NIC Settings

If possible, use SR-IOV for better performance, as explained in the following topics:


  • Changing module parameters for an SR-IOV driver requires an ESXi host reboot.
  • Disable physical NIC interrupt moderation on ESXi host as follows:
    # esxcli system module parameters set -m ixgbe -p "InterruptThrottleRate=0“
  • If you enable multiqueue support, you must also enable Receive-Side Scaling (RSS) for the driver.
    • To enable RSS, set the port value to 4.
    • Specify ports in a comma-separated string.
    Example—Set 3 NICs with 2 ports each.
    $ vmkload_mod -u ixgbe esxcli system module parameters set -m ixgbe -p RSS=”4,4,4,4,4,4”
    $ vmkload_mod ixgbe RSS=”4,4,4,4,4,
    Example—Set RSS for a single port:
    $ vmkload_mod -u ixgbe esxcli system module parameters set -m ixgbe -p RSS=”0,4,0,0,0,0”

VMXNET3/vSwitch and Virtual Interrupt Coalescing

By default, VMXNET3 supports an interrupt coalescing algorithm (for the same reasons that physical NICs implement interrupt moderation). To avoid flooding the host system with too many interrupts, packets are collected and one single interrupt is generated for multiple packets. This is called interrupt coalescing.
Interrupt coalescence refers to the amount of traffic that a network interface receives, or the amount of time that passes after traffic is received, before you issue a hard interrupt. Interrupting too soon or too frequently results in poor system performance, as the kernel stops (or “interrupts”) a running task to handle the interrupt request from the hardware. Interrupting too late can result in traffic loss if the traffic is not taken off the NIC soon enough—more traffic arrives, overwriting the previous traffic still waiting to be received into the kernel.To disable this functionality through the vSphere Web Client, go to
VM Settings
Advanced General
Configuration Parameters
and add an entry for
with the value
To disable virtual interrupt coalescing for all virtual NICs on the host (which affects all VMs, not just the latency-sensitive ones), set the advanced networking performance option. Go to
Advanced Settings
and set

Enable Multiqueue Support on Intel x710/x520

Use ESXi 6.0.0 or later, with an ixgbe driver version with multiqueue support. See SR-IOV Driver Versions in the Compatibility Matrix. Modify the
file or access
Advanced Settings
to enable multiqueue support:
ethernetX.pnicFeatures = “4”
To set multi-core affinity so a vSwitch can exceed 300K PPS, set:
ethernetX.pnicFeatures = "4" ethernetX.ctxPerDev = "1"
ethernetX.ctxPerDev = “1”
, is like a binary flag (set to 1 to enable). This binary flag adds a CPU thread to process traffic only from the port
. This leads to improved traffic scheduling performance.

NUMA and Resource Considerations

NUMA is Non-Uniform Memory Access. Multi-Core processors have complicated designs. To tackle performance issues in such systems, you need to be aware of all NUMA and CPU Pinning nuances. Vital aspects to look for:
  • Which cores are our threads are running on? (if hyperthreading is enabled, check Hyperthreading)
  • Which cores are our vCPUs are running on? (affinity)
  • In which NUMA socket is the physical NIC card installed?
  • Where has memory been allocated? (NUMA effects)
    Threads running on any socket see one unified memory space – therefore they can read/write to memory that is local to other Sockets.
  • Is memory shared between different sockets on a node?
  • It takes more time to access memory on different sockets than it takes to access local memory.
    NUMA effects occur when threads excessively access memory on a different NUMA domain. To avoid cross-NUMA issues, avoid Quick Path Interconnect (QPi) between Socket 0 communication and Socket 1.
For latency-sensitive VMs like PA-VM, VMware recommends that you do not over-commit vCPUs as compared to the number of physical CPUs (processors) on the ESXi host. For example, if the host has 8 CPU cores, limit the number of vCPUs for your VM to 7. This ensures that the ESXi VMkernel scheduler has a better chance of placing the vCPUs on pCPUs that won’t contend with other scheduling contexts, such as vCPUs from other VMs or ESXi helper worlds. It is a good practice to ensure that the number of vCPUs you allocate to the VM does not exceed the number of active CPU-consuming processes or threads in the VM.
For best performance, all vCPUs should be scheduled on the same NUMA node and all VM memory should fit and be allocated out of the local physical memory attached to that NUMA node. This can be changed using the VM setting
numa.nodeAffinity=0, 1, …
where 0, 1, and so forth, are the socket numbers.
To ensure that the VM gets exclusive access to the CPU resources, set Latency Sensitivity to High. For the new setting to take effect, the VM CPU reservation must be set to maximum, Memory should be reserved, and the CPU limit must be set to unlimited.
  • In newer versions, use the vSphere Web Client to set the VM Latency Sensitivity option to High (the default is Normal).
  • In older versions, set
    to High.
Additionally, VM’s vCPUs can be pinned to host CPU cores using the VM setting
Host Affinity
so that it is never scheduled to different cores. Keep NUMA and hyperthreading in mind when you use Host Affinity. Avoid setting Host Affinity if the system is over committed. For more detail see Potential Issues with CPU Affinity.
After you implement the tuning parameters, use esxtop or CPU charts to check CPU Ready (%RDY) and Co Stop (%CSTP) for the VM. Both values should be close to 0% to ensure exclusive access to CPU resources. You can also use esxtop to check for NUMA usage and ensure memory resources for the VM are not spread across NUMA nodes. For more detail, see Interpreting esxtop Statistics.

Use Cases

Use Case 1: vSwitch Deployment

The figure below shows a deployment of a PA-VM on an ESXi host where the data ports “Port 1” and “Port 2” are linked to eth1 and eth2 of the PA-VM. Each port hosts two queue pairs (for example, Tx0/Rx0, and Tx1/Rx1) or has multiqueue enabled.
Enabling multiqueue and RSS for load balancing packets sent/received to/from multiple queues enhances processing performance. Based on an internal logic of vCPU to port/queue mapping (in this case) packets arriving and being sent out from P1/Q0 and P2/Q0 are processed by dataplane task T1 running on (i.e., pinned to) vCPU1. The data plane task T2 follows a similar association, as shown in the vSwitch deployment diagram above.
The two data plane tasks are running on vCPU1 and vCPU2 and these are non-sibling CPUs (means that they do not share the same core in case of hyperthreading). This means that even with hyperthreading enabled the task assignment can be pinned to different cores for high performance. Also these dataplane task vCPUs all belong to the same NUMA node (or socket) to avoid NUMA-related performance issues.
Two other performance bottlenecks can be addressed with increasing the queue sizes and dedicating a vCPU or thread to the ports that schedule traffic to and from these ports. Increasing the queue sizes (Qsize) will accommodate large sudden bursts of traffic and prevent packet drops under bursty traffic. Adding a dedicated CPU thread (
ethernetX.ctxPerDev = 1
) to port level packet processing will allow traffic to be processed at a higher rate, thereby increasing the traffic throughput to reach line rate.
The PA-VM packet processing technique also determines performance. This can be set to either DPDK or PacketMMAP. DPDK uses a poll mode driver (depends on the driver type) to constantly poll for packets received in the queues. This leads to higher throughput performance. Depending on the poll period is latency observed by the packets. If the polling is continuous (i.e., busy-poll a setting from the PANOS cli) then the vCPU utilization for the data plane tasks will be a 100% but will yield the best performance. Internally the software uses a millisecond-level polling time to prevent unnecessary utilization of CPU resources.
PacketMMAP, on the other hand, has a lower performance than DPDK but it works with any network level drivers. For DPDK the vSwitch driver must have support for DPDK. PacketMMAP works with interrupts that are raised when a packet is received by the port and placed in the receive queue. This means that for every packet, or group of packets, interrupts are raised and packets are drained off the receive queue for processing. This results in lower latency in packet processing, but reduced throughput, because interrupts must be processed every time, causing higher CPU overhead. In general PacketMMAP will have lower packet processing latency than DPDK (without busy poll modification).

Use Case 2: SR-IOV Deployment

The SR-IOV diagram below shows a PAVM deployment similar to the vSwitch use case, but in SR-IOV mode.
In SR-IOV the compatible physical NIC port (manifests as a Physical Function) is essentially carved out into multiple interfaces (manifests as Virtual Functions). The figure above shows that NIC1 Port1 has a VF named VFX that is associated as one of the PAVM dataplane interfaces — eth1, for example. A similar association is created for Port2 VF to PAVM eth2.The chain of packet processing is similar to that of the deployment in the vSwitch environment. The only difference is that the SR-IOV VF drivers should be compatible with those used in PAN-OS. Also, since there is no internal vSwitch (in the host) switching traffic, there is no need to set a dedicated thread for traffic scheduling from a port (that is,
ethernetX.ctxPerDev = 1
is not required in this setting). Interfaces with SR-IOV and DPDK will yield even higher packet processing performance than the vSwitch use case.

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