linux-kernel - Is kernel/Kconfig.hz still up-to-date?

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Message-Id: <D90FWJ3O72ML.2DA83AXPJCR3Q@cknow.org>
Date: Mon, 07 Apr 2025 15:27:21 +0200
From: "Diederik de Haas" <didi.debian@...ow.org>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Christoph Lameter"
 <cl@...ux.com>, "Andrew Morton" <akpm@...ux-foundation.org>, "Thomas
 Gleixner" <tglx@...utronix.de>
Cc: <linux-kernel@...r.kernel.org>, "Bagas Sanjaya" <bagasdotme@...il.com>,
 "Dang Huynh" <danct12@...eup.net>
Subject: Is kernel/Kconfig.hz still up-to-date?

Hi,

I recently had a discussion about the use of HZ_1000 in the kernel
configuration and the impact on performance.
My reading of the HZ_1000 help text tells me that HZ_1000 is primarily
useful for DAW and other systems where RT capabilities are (most)
important. This is due to "systems requiring fast interactive responses
to events", whereby I put the emphasis on *requiring*.

As *I* understand the rest of the help texts, a higher Hz value can/will
have a negative effect on f.e. IO performance. And I'm not entirely
sure, but it seems each CPU (core?) multiplies the nr of interrupts?

But, doing a ``git blame`` on the choices shows that apart from a
spelling fix in 2025, all the text hasn't changed since 2005/2006.
But a LOT has changed since then. There are more architectures and the
hardware and the kernel itself have changed quite a bit since then.

While the Kconfig.hz default is still HZ_250, the x86 defconfig changed
to HZ_1000 in 5cb04df8d3f0 ("x86: defconfig updates") (in 2008) and
there are various distros which have switched to HZ_1000.

So my questions are: are the Kconfig help text still accurate for
current (hardware) systems and kernels? Is HZ_250 still the most
sensible default? Or is the 'newer' HZ_300 better? Or even HZ_1000?
And does that apply only for x86 or for all architectures?
(distros seem to vary between architectures f.e.)

Cheers,
  Diederik

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