On Thu, 2005-07-14 at 17:24 -0700, Linus Torvalds wrote:
>
> On Thu, 14 Jul 2005, Lee Revell wrote:
>
> Trust me. When I say that the right thing to do is to just have a fixed
> (but high) HZ value, and just changing the timer rate, I'm -right-.
>
> I'm always right. This time I'm just even more right than usual.
Of course you are, jiffies are simple and efficient.
But it may be worthwhile to provide better/simpler API for relative
timeouts and also better hide the implementation details of the tick
system.
If i sum-up the discussion from my POV:
- use a 32-bit tick counter on 32-bit platforms and use a 64-bit counter
on 64-bit platforms
- keep the constant HZ=1000 (mS resolution) on 32-bit platforms
- remove the assumption that timer interrupts and jiffies are 1:1 thing
(jiffies may be incremented by >1 ticks at timer interrupt)
- determine jiffies_increment at boot
- have a slow clock mode to help power management (adjust
jiffies_increment by the slowdown factor)
- it may be useful to bump up HZ to 1e6 (uS res.) or 1e9 (nS res.) on
64-bit platforms, if there are benefits such as better accuracy during
time units conversions or if a higher frequency timer hardware is
available/viable.
- it may be also useful to bump HZ on -RT (Real-time) kernels, or with
-HRT (High-resolution timers support). Users of those kernel are willing
to pay the cost of the overhead to have better resolution
- avoid direct usage of the jiffies variable, instead use jiffies()
(inline or MACRO), IMO monotonic_clock() would be a better name
- provide a relative timeout API (see my previous post, or Alan's
suggestions)
- remove most of the direct use of jiffies through the code and replace
them with msleep(), relative timer, etc
- use human units for those APIs
- Eric St-Laurent
-
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