Re: [PATCH] Kconfig.hz: Change default HZ to 1000

Ingo Molnar
2025-02-23T10:00:36Z

* Andrea Righi <arighi@nvidia.com> wrote:

> On Wed, Feb 12, 2025 at 09:50:54AM -0500, Joel Fernandes wrote:
> > On Mon, Feb 10, 2025 at 12:19:15AM +0000, Qais Yousef wrote:
> ...
> > > I believe HZ_250 was the default as a trade-off for battery power
> > > devices that might not be happy with frequent TICKS potentially draining
> > > the battery unnecessarily. But to my understanding the current state of
> >
> > Actually, on x86, me and Steve did some debug on Chromebooks and we found
> > that HZ_250 actually increased power versus higher HZ. This was because
> > cpuidle governor changes C states on the tick, and by making it less
> > frequent, the CPU could be in a shallow C state for longer.
>
> FWIW, I found the same about power consumption when we decided to switch to
> CONFIG_HZ=1000 in the Ubuntu kernel:
> https://discourse.ubuntu.com/t/enable-low-latency-features-in-the-generic-ubuntu-kernel-for-24-04/42255

The "HZ=1000 reduces power consumption or keeps it the same" is
actually a pretty good argument to change the default to HZ=1000.

These experiments and numbers (if any) should be incorporated in the
changelog prominently - as actual data and the Kconfig decisions made
by major distros will, most of the time, be superior to meta analysis
that seems to be the changelog right now.

Thanks,

Ingo