Re: The "best" value of HZ

[Jesper Juhl]

On 10/28/05, Lee Revell <rlrevell@xxxxxxxxxxx> wrote:
> On Fri, 2005-10-28 at 03:31 +0100, Alistair John Strachan wrote:
> > On Friday 28 October 2005 00:18, Claudio Scordino wrote:
> > > Hi,
> > >
> > >     during the last years there has been a lot of discussion about the
> > > "best" value of HZ... On i386 was 100, then became 1000, and finally was
> > > set to 250. I'm thinking to do an evaluation of this parameter using
> > > different architectures.
> > >
> > > Has anybody thought to give the possibility to modify the value of HZ at
> > > boot time instead of at compile time ? This would allow to easily test
> > > different values on different machines and create a table containing the
> > > "best" value for each architecture...  At this moment, instead, we have to
> > > recompile the kernel for each different value :(
> > >
> > > Do you think there would be much work to do that ?
> > > Do you think it would be a desired feature the knowledge of the best value
> > > for each architecture with more precision ?
> >
> > Google for "dynticks". There's obviously an overhead associated with HZ not
> > being a constant (the compiler cannot optimise many expressions), but the
> > feature is being worked on nonetheless.
> >
>
> Well Linus had the best idea in that thread (as usual) which was to
> implement "dynamic ticks" by leaving HZ a constant, setting it to a high
> value, and skipping ticks when idle.  Has there been any work in that
> direction?
>

i did a bit of work in that area, but the stuff I came up with never
seemed to work right, so I dropped it.


--
Jesper Juhl <jesper.juhl@xxxxxxxxx>
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