Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt

[Krzysztof Halasa]

Linus Torvalds <torvalds@xxxxxxxx> writes:

> And in short-term things, the timeval/jiffie conversion is likely to be a 
> _bigger_ issue than the crystal frequency conversion.
>
> So we should aim for a HZ value that makes it easy to convert to and from
> the standard user-space interface formats. 100Hz, 250Hz and 1000Hz are all
> good values for that reason. 864 is not.

Probably only theoretical, and probably the hardware isn't up to it...
But what if we have:
- 64-bit jiffies done in hardware (a counter). 1 cycle = 1 microsecond
  or even a CPU clock cycle. Can *APIC or another HPET do that?
- 64-bit "match timer" (i.e., a register in the counter which fires IRQ
  when it matches the counter value)
- the CPU(s) sorting the timer list and programming "match timer" with
  software timer next to be executed. Upon firing the timer, a new "next
  to be executed" timer would be programmed into the counter's "match
  timer".

We would have no timer ticks when nobody requested them - the CPUs would
be allowed to sleep for, say, even 50 ms when no task is RUNNING.
-- 
Krzysztof Halasa
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