Re: PIT, HZ, and devices

[Tom Bradley <tbradley@jaycor.com>]

It doesn't sound like a good idea to me. For one, any timing that is 
dependant upon this will be off. I do believe that uptime and sleep are 
dependant on jiffies which is incremented by the PIT (correct me if I am 
wrong).  It is also the interrupt that decrements your time quantum for 
scheduling. By changing the HZ value you will be changing your systems 
performance. 

Tom

On Saturday 02 February 2002 10:54 pm, you wrote:
> Hi!
>
> I've been working on the programmable interrupt controller (x86, maybe
> mips) and have been making a rough device outline, as i think it would be
> nice to have dynamic HZ (allows the kernel to be quick and responsive, or
> less responsive but a bit more efficient).  in the event of coding up a
> simple proof of concept, i noticed that many drivers (ftape, ide, setup,
> etc) also deal with setting/modifying the pit.  this gets messy when the
> pit is readonly (as i believe it is.  reading only returns current count,
> not the divisor value to rederive HZ).  i am considering changing the code
> to access a kernel-common system to access the clock, rather than have the
> current model where all code messes with the clock itself (most of which
> just reads a timestamp or resets to 100hz mode).
>
> is it completely a waste of time to try to make this all work, or is it
> maybe something to consider?  i imagine it would make the kernel a bit more
> dynamic, but it's also a pretty small thing to be dealing with.
>
> I understand the placebo that floows cranking HZ up to something fast, and
> I am not after that.  I am writing some applications that could make use of
> having more interrupts for less latency.  a limited set of functionality,
> not worth hardcoding HZ to 1000 for, but realyl helpful when it's
> necessary.
>
> thanks =)
> christopher p wright
>
>
>
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