[QUESTION] kernel/Kconfig.hz: outdated help texts?

[QUESTION] kernel/Kconfig.hz: outdated help texts?

[torvic9]

Hello,

I noticed that the help text in kernel/Kconfig.hz has barely changed since
configurable frequency of the timer was introduced in 2005.

Are these help texts still accurate 21 years later?

We have e.g.:

  "250 Hz is a good compromise choice allowing server performance
   while also showing good interactive responsiveness even
   on SMP and NUMA systems. If you are going to be using NTSC video
   or multimedia, select 300 Hz instead."

Is that NTSC/PAL thing still relevant today, in times of high resolution timers,
modern graphics cards, Freesync and high-refresh 4K monitors with 144 Hz?

Cheers,

Tor Vic

Re: [QUESTION] kernel/Kconfig.hz: outdated help texts?

[Nathan Chancellor]

On Fri, Apr 24, 2026 at 10:18:44AM +0200, torvic9@mailbox.org wrote:
> Hello,
> 
> I noticed that the help text in kernel/Kconfig.hz has barely changed since
> configurable frequency of the timer was introduced in 2005.
> 
> Are these help texts still accurate 21 years later?
> 
> We have e.g.:
> 
>   "250 Hz is a good compromise choice allowing server performance
>    while also showing good interactive responsiveness even
>    on SMP and NUMA systems. If you are going to be using NTSC video
>    or multimedia, select 300 Hz instead."
> 
> Is that NTSC/PAL thing still relevant today, in times of high resolution timers,
> modern graphics cards, Freesync and high-refresh 4K monitors with 144 Hz?
> 
> Cheers,
> 
> Tor Vic

I think this message would be better directed at the timekeeping folks
(now CC'd), rather than Kbuild/Kconfig.

Cheers,
Nathan

Re: [QUESTION] kernel/Kconfig.hz: outdated help texts?

[John Stultz]

On Fri, Apr 24, 2026 at 11:30 AM Nathan Chancellor <nathan@kernel.org> wrote:
> On Fri, Apr 24, 2026 at 10:18:44AM +0200, torvic9@mailbox.org wrote:
> > Hello,
> >
> > I noticed that the help text in kernel/Kconfig.hz has barely changed since
> > configurable frequency of the timer was introduced in 2005.
> >
> > Are these help texts still accurate 21 years later?
> >
> > We have e.g.:
> >
> >   "250 Hz is a good compromise choice allowing server performance
> >    while also showing good interactive responsiveness even
> >    on SMP and NUMA systems. If you are going to be using NTSC video
> >    or multimedia, select 300 Hz instead."
> >
> > Is that NTSC/PAL thing still relevant today, in times of high resolution timers,
> > modern graphics cards, Freesync and high-refresh 4K monitors with 144 Hz?
> >

I believe the rationale there was just that the math for 60fps worked
better w/ HZ=300, as it gave you 5 ticks per frame rather than the
4.1666.. HZ=250 gives you.

hrtimers obviously makes this less critical, but it might be worth
some consideration as I know as framerates have gotten higher on
devices, using HZ=250 has been a pain point - as at 120fps, you only
8.333ms per frame and with HZ=250 the 4ms ticks doesn't give much time
(2.083 ticks) for cpu balancing to fix things if task wakeup placement
was not ideal.  That said HZ=300 doesn't really help much there, since
at 120fps you get 2.5 ticks, which is basically the same.

So for 60fps, I think HZ=300 might provide some benefit (which would
align with the Kconfig description), but I don't have any real world
numbers to show that at the moment.

thanks
-john