# Customizing CPUSET

CPUSET in the `/etc/scylla.d/cpuset.conf` file is automatically configured by running the `scylla_setup`
(or `scylla_cpuset_setup`) script. If you want to customize CPUSET, you must modify both the `cpuset.conf`
and `perftune.yaml` files.

Note that the `scylla-server` service will generate `/etc/scylla.d/perftune.yaml` *only if* the file doesn’t exist.

## Examples

Here are a few examples of possible configurations. In the examples, `eth5` is used as a NIC name and `/var/lib/scylla` as a data directory.

### Example 1

* 16 CPUs system.
* You want to run ScyllaDB on CPUs 3, 4, 5, and have IRQs handled on the same CPUs, while allowing other apps on the same machine to benefit
  from XFS/RFS/RPS from `eth5`.

**cpuset.conf:**

```none
CPUSET="--cpuset 3,4,5 "
```

**perftune.yaml:**

```none
cpu_mask: '0xffff'
dir:
- /var/lib/scylla
irq_cpu_mask: '0x38'
nic:
- eth5
tune:
- net
- disks
```

### Example 2

* 16 CPUs system.
* You want to run ScyllaDB on CPUs 3, 4, 5, and have IRQs handled on the same CPUs, and ScyllaDB is going to be the only application
  that will use `eth5`.

**cpuset.conf:**

```none
CPUSET="--cpuset 3,4,5 "
```

**perftune.yaml:**

```none
cpu_mask: '0x38'
dir:
- /var/lib/scylla
irq_cpu_mask: '0x38'
nic:
- eth5
tune:
- net
- disks
```

### Example 3

* 16 CPUs system.
* You want to run ScyllaDB on CPUs 3, 4, 5, and IRQs handled on CPUs 6,7,8, while allowing other apps on the same machine to benefit
  from XFS/RFS/RPS from `eth5`.

**cpuset.conf:**

```none
CPUSET="--cpuset 3,4,5 "
```

**perftune.yaml:**

```none
cpu_mask: '0xffff'
dir:
- /var/lib/scylla
irq_cpu_mask: '0x1c0'
nic:
- eth5
tune:
- net
- disks
```