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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <Z7rxuqIB38Wv557A@gmail.com>
Date: Sun, 23 Feb 2025 11:00:26 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	Qais Yousef <qyousef@...alina.io>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Stultz <jstultz@...gle.com>,
	Saravana Kannan <saravanak@...gle.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Frederic Weisbecker <frederic@...nel.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Kconfig.hz: Change default HZ to 1000


* Andrea Righi <arighi@...dia.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