How does BORE scheduler go along with the linux-zen patches?

[mabod]

I am currently looking into linux-tkg kernel. They provide a config option for the BORE scheduler as well as for the linux-zen kernel patches to modify CFS settings.

linux-zen aims to improve latency and responsiveness of the CFS kernel. And so does the BORE scheduler. Should they both be applied? What is the recommendation?

[firelzrd]

Hi there.

In my understanding, to the CFS scheduler, Zen is a series of modification of tuning knobs.
It does not change CFS's algorithms.

BORE is a modification to CFS's algorithm.

I have never read through the Zen patch, or talked to the tkg team about their patches, so I do not know exactly why tkg provides two different options, but here's my guess:

Zen modifies CFS in some of the sysctl tuning knobs. So does BORE.
So the tkg team left the user which patch's values to adopt.

[mabod]

Your reply indicates to me that I should better use BORE without the ZEN patches. Because BORE is already optimized for low latency in itself.

[firelzrd]

I want you to keep in your mind that what I've said applies to CFS tunables only.
"Zen Interactive Tuning" includes a lot more than just CFS tuning, so if tkg incorporates the whole Zen patchset not just scheduler-wise, and if you prefer responsiveness over throughput, then you probably should also opt in to include Zen, not only BORE.

[mabod]

From what I see tkg is only including "interactivity" variables from ZEN.
Like

sysctl_sched_idle_min_granularity
sched_nr_latency
sysctl_sched_cfs_bandwidth_slice
etc.

So I will stop using that for kernels with the BORE scheduler.

[ptr1337]

You can also just test these settings if they suit to you.
@firelzrd made a little tool, to switch between the CFS sysctl values with some presets:
https://github.com/CachyOS/CachyOS-Settings/blob/master/usr/bin/tunecfs2

Be sure you have ruby installed when you use it.

[raykzhao]

Hi @mabod,

I think bore scheduler should be able to work with zen patches together, as long as you do one of the following:

1. Apply the full bore scheduler patch and the zen patch without zen-kernel/zen-kernel@8fcf775
2. Apply the bore scheduler patch without sysctl and the full zen patch

You can test which option works better for your workload.