Re: [RFC PATCH 0/2] sched/fair: Remove tunable scaling

[Vincent Guittot]

On Fri, 2 Oct 2026 at 14:45, Tor Vic <torvic9@xxxxxxxxxxx> wrote:
>
> This series removes the scaling of tunables, which was introduced around
> Linux 2.6.33.
>
> I split this into two separate patches:
>
> The first removes the "none" and "linear" scaling which are likely not used much
> and have limited usefulness, as one can always set sched_base_slice through
> debugfs.

How did you reach this conclusion? and why it's worth removing it

> It keeps the logarithmic scaling which is already the default.
>
> The second removes the entire scaling mecanism and sets a fixed sched_base_slice
> of 2 milliseconds, a value which has been chosen somewhat arbitrarily.

No, the sysctl_sched_base_slice value has not been chosen arbitrarily
and the commit you mentioned below gives you the reason

>
> Currently, the base_slice multiplied by the log2 factor can take the values of
> 0.7 (1 CPU), 1.4 (2-3 CPUs), 2.1 (4-7 CPUs) and 2.8 msecs (8+ CPUs), so it seems
> that the new value of 2 msecs is a sane default, which I also use on my consumer
> x86_64 machines.
> However I'll leave that open for discussion. Note that the base_slice value has
> changed quite often over the years, lastly in 2025 [1].
>
> The series applies to 7.3-rc5, and is build- and boot tested on a measly 2C/4T
> Skylake machine. I marked it as RFC because I don't know whether these changes
> are actually wanted by the sched people - and because I'm not a developer.
> It does however remove quite a lot of code.
>
> [1] commit 2ae891b826958b60919ea21c727f77bcd6ffcc2c
>
> Tor Vic (2):
>   sched/fair: Remove the 'none' and 'linear' scaling of tunables
>   sched/fair: Remove sched_base_slice scaling altogether
>
>  include/linux/sched/sysctl.h |  7 ----
>  kernel/sched/core.c          |  1 -
>  kernel/sched/debug.c         | 52 ------------------------
>  kernel/sched/fair.c          | 79 ++----------------------------------
>  kernel/sched/sched.h         |  5 ---
>  5 files changed, 3 insertions(+), 141 deletions(-)
>
> --
> 2.55.0
>