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


On Thu, 14 Jul 2005, Vojtech Pavlik wrote:
>
> A note on the relaive timer API: There needs to be a way to say
> "x milliseconds from the time this timer should have triggered" instead
> of "x milliseconds from now", to avoid skew in timers that try to be
> strictly periodic.

I disagree.

There should be an _absolute_ interface, and a driver that wants that
should just have calculated when in time the timeout finishes - and then
keep on using the absolute value.

Btw, this is exactly why the jiffy-based thing is _good_. The kernel
timers _are_ absolute, and you make them relative by adding "jiffies".

The fact is, the current timers are better than people give them credit
for, and converting them away from a jiffies-based interface (to a
usleep-like one) is STUPID.

There's absolutely nothing wrong with "jiffies", and anybody who thinks
that

msleep(20);

is fundamentally better than

timeout = jiffies + HZ/50;

just doesn't realize that the latter is a bit more complicated exactly
because the latter is a hell of a lot more POWERFUL. Trying to get rid of
jiffies for some religious reason is _stupid_.

I have to say, this whole thread has been pretty damn worthless in general
in my not-so-humble opinion.

Linus
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