Longhorn now supports configurable CPU cores for the V2 data engine through the use of a CPU Mask. This mask allows you to define exactly which CPU cores are allocated to the engine, offering both global and per-node configuration options.

Understanding the CPU Mask

The CPU mask is a hexadecimal (hex) representation of a binary bitmask, where each bit corresponds to a specific CPU core.

• A bit set to 1 means the core is enabled for the data engine.
• A bit set to 0 means the core is skipped.

How to Calculate the Mask

To determine the correct hex string, visualize your CPU cores as a sequence of bits from right to left:

Example for 23 Cores: To allocate 23 cores, you need 23 bits set to 1.

• Binary: 111 1111 1111 1111 1111 1111
• Hexadecimal: 0x7FFFFF

Note: Do not confuse the number of cores with the hex value. For instance, setting 0x4 (Binary 0100) only enables one core (Core #2), whereas 0xF (Binary 1111) enables four cores.

Global Configuration

To set CPU cores globally across the cluster, update the data-engine-cpu-mask setting.

1. Navigate to Settings > General.
2. Locate Data Engine CPU Mask.
3. Enter your calculated hex string (for example, 0xF).

Per-node Configuration

For node-specific CPU core allocation, update the spec.dataEngineSpec.v2.cpuMask field of the instance manager with a hexadecimal encoded string. By default, this value is empty, and the v2 data engine will use the global setting specified by data-engine-cpu-mask. When a per-node configuration is set, the v2 data engine will prioritize this value over the global setting for that specific node.

Calculation Tools

You can use a Binary to Hex Converter to help calculate your mask. Type a 1 for every core you wish to allocate and convert the resulting binary string to Hex.