Re: dynamic-hz

Pavel Machek
2004-12-12T16:38:05Z

Hi!

> The below patch allows to set the HZ dynamically at boot time with
> command line parameter. HZ=1000 HZ=100 HZ=333 any other value just works
> (though certain value may cause more or less drift to the system time
> advance/decrease).
>
> Is there any interest from the mainline developers to merge this into
> 2.6? I'm getting requests for this feature being forward ported to
> 2.6 (both for batch jobs and for the powersaved that can trim the hz
> down to 80mhz). It should be up to the user to choose the HZ like it was
> in 2.4-aa.
>
> This patch is quite intrusive since many HZ visible to userspace have to
> be converted to USER_HZ, and most important because HZ isn't available
> at compile time anymore and every variable in function of HZ must be
> either changed to be in function of USER_HZ or it must be initialized at
> runtime. The code has debugging code (optional at compile time) so that
> I can guarantee that there cannot be any regression.
>
> Technically this makes a lot of sense to me (well, you can guess why I
> implemented it in the first place), at least in archs where one cannot
> reprogram the timer chip in a performant way (to stop timer ticks
> completely until the next posted timer). This is in production for years
> in SLES8 btw.
>
> http://www.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa3/9999_zzz-dynamic-hz-5.gz

It certainly helps with singing capacitors... What is overhead of
this?

Pavel
--
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