Re: HZ, preferably as small as possible

Linus Torvalds
2002-07-15T18:57:07Z

On 15 Jul 2002, Robert Love wrote:
>
> A cleaner solution to this issue is a higher resolution timer, e.g. the
> high-res-timers project which has high resolution POSIX timers.

But that really doesn't solve the problem either.

You still need to have some limit on the timer resolution. Whether you
call that limit "HZ" or something else is irrelevant in the end. Just
calling them "high-resolution" doesn't make the problem go away, you still
have some resolution (*).

So once you set some magic limit on the fine-grained resolution (let's
call that "MAX_FINE_HZ"), you might as well realize that that really is
100% equivalent to just making HZ _be_ that value. Together with possibly
making the actual timer tick happen at a slower rate according to some
other heuristics (ie "the system doesn't need timers right now, let's just
not do them").

Linus

(*) Which is a lot less than the hw can generate, since you mustn't allow
users to bog down the system in timer interrupts by just using
"itimer(ITIMER_REAL, .. fine-resolution..)".