# Performance Tips

## Performance Tips

{% hint style="danger" %}
This website/page will be End-of-life (EOL) after 31 August 2024. We recommend you to visit [OpenEBS Documentation](https://openebs.io/docs/user-guides/replicated-storage-user-guide/replicated-pv-mayastor/rs-installation) for the latest Mayastor documentation (v2.6 and above).

Mayastor is now also referred to as OpenEBS Replicated PV Mayastor.
{% endhint %}

### CPU isolation

Mayastor will fully utilize each CPU core that it was configured to run on. It will spawn a thread on each and the thread will run in an endless loop serving tasks dispatched to it without sleeping or blocking. There are also other Mayastor threads that are not bound to the CPU and those are allowed to block and sleep. However, the bound threads (also called reactors) rely on being interrupted by the kernel and other userspace processes as little as possible. Otherwise, the latency of IO may suffer.

Ideally, the only thing that interrupts Mayastor's reactor would be only kernel time-based interrupts responsible for CPU accounting. However, that is far from trivial. `isolcpus` option that we will be using does not prevent:

* kernel threads and
* other k8s pods to run on the isolated CPU

However, it prevents system services including kubelet from interfering with Mayastor.

#### Set Linux kernel boot parameter

Note that the best way to accomplish this step may differ, based on the Linux distro that you are using.

Add the `isolcpus` kernel boot parameter to `GRUB_CMDLINE_LINUX_DEFAULT` in the grub configuration file, with a value which identifies the CPUs to be isolated (indexing starts from zero here). The location of the configuration file to change is typically `/etc/default/grub` but may vary. For example when running Ubuntu 20.04 in AWS EC2 Cloud boot parameters are in `/etc/default/grub.d/50-cloudimg-settings.cfg`.

In the following example we assume a system with 4 CPU cores in total, and that the third and the fourth CPU cores are to be dedicated to Mayastor.

```
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=2,3"
```

#### Update grub

{% tabs %}
{% tab title="Command" %}
```bash
sudo update-grub
```
{% endtab %}

{% tab title="Output example" %}
```
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/40-force-partuuid.cfg'
Sourcing file `/etc/default/grub.d/50-cloudimg-settings.cfg'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.8.0-29-generic
Found initrd image: /boot/microcode.cpio /boot/initrd.img-5.8.0-29-generic
Found linux image: /boot/vmlinuz-5.4.0-1037-aws
Found initrd image: /boot/microcode.cpio /boot/initrd.img-5.4.0-1037-aws
Found Ubuntu 20.04.2 LTS (20.04) on /dev/xvda1
done
```
{% endtab %}
{% endtabs %}

#### Reboot the system

{% tabs %}
{% tab title="Command" %}
```bash
sudo reboot
```
{% endtab %}
{% endtabs %}

#### Verify isolcpus

Basic verification is by outputting the boot parameters of the currently running kernel:

{% tabs %}
{% tab title="Command" %}
```bash
cat /proc/cmdline
```
{% endtab %}

{% tab title="Example output" %}
```
BOOT_IMAGE=/boot/vmlinuz-5.8.0-29-generic root=PARTUUID=7213a253-01 ro console=tty1 console=ttyS0 nvme_core.io_timeout=4294967295 isolcpus=2,3 panic=-1
```
{% endtab %}
{% endtabs %}

You can also print a list of isolated CPUs:

{% tabs %}
{% tab title="Command" %}
```bash
cat /sys/devices/system/cpu/isolated
```
{% endtab %}

{% tab title="Example output" %}
```
2-3
```
{% endtab %}
{% endtabs %}

#### Deploy Mayastor daemonset

Edit the `mayastor-daemonset.yaml` file and set the `-l` parameter of mayastor to specify CPU cores that Mayastor reactors should run on. In the following example we run mayastor on the third and fourth CPU core:

```yaml
  ...
  containers:
    - name: mayastor
      ...
      args:
        ...
        - "-l3,4"
```

## <<<<<<< HEAD

In the above command, `io_engine.coreList={3,4}` specifies that Mayastor's reactors should operate on the third and fourth CPU cores.

> > > > > > > ef5f92a (docs: added EOL info panel (#216))
