1.4.4. Optimizing performanceΒΆ

To get the best performance, we need to isolate the CPUs reserved to the fast path from all other userland process and kernel threads. The most efficient way to achieve this, is to boot the hypervisor kernel with isolcpus, nohz_full and rcu_nocbs options.

These options must be added to the GRUB_CMDLINE_LINUX variable in /etc/default/grub. They should contain the same CPU list as in FP_MASK from /etc/fast-path.env.

# fp-conf-tool -D -F | grep FP_MASK
FP_MASK=4-7,12-15
# vi /etc/default/grub
...
GRUB_CMDLINE_LINUX="crashkernel=auto console=ttyS0,115200n8 \
  isolcpus=4-7,12-15 nohz_full=4-7,12-15 rcu_nocbs=4-7,12-15"
...

Then issue the following command as root to update the grub install:

  • on BIOS-based machines:

    # grub2-mkconfig -o /boot/grub2/grub.cfg

  • on UEFI-based machines:

    # grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg