Performance Tips

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 do the following step may differ based on Linux distro that you are using.

Add isolcpus kernel boot parameter to GRUB_CMDLINE_LINUX_DEFAULT in the grub configuration file with the specification of isolated CPUs (indexing starts from zero here). The location of the configuration file to change is /etc/default/grub, though it depends. 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 and the third and the fourth CPU core will be dedicated for Mayastor.

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=2,3"

Update grub

Output example
sudo update-grub
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

Reboot the system

sudo reboot

Verify isolcpus

Basic verification is to print the boot parameters of the currently running kernel.

Example output
cat /proc/cmdline
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

You could also print a list of isolated CPUs.

Example output
cat /sys/devices/system/cpu/isolated
Example output

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:

- name: mayastor
- "-l3,4"