Re: dynamic-hz

Tony Lindgren
2004-12-14T23:07:02Z

* Pavel Machek <pavel@suse.cz> [041214 14:07]:
> Hi!
>
> > > > The patch in question is at:
> > > >
> > > > http://linux-omap.bkbits.net:8080/main/user=tmlind/patch@1.2016.4.18?nav=!-|index.html|stats|!+|index.html|ChangeSet@-12w|cset@1.2016.4.18
> > >
> > > Wow, that's basically 8 lines of code plus driver for new
> > > hardware... Is it really that simple?
> >
> > Yeah, the key things are reprogramming the timer in the idle loop
> > based on next_timer_interrupt(), and calling timer_interrupt from
> > other interrupts as well :)
> >
> > Should we try a similar patch for x86/amd64? I'm not sure which timers
> > to use though? One should be programmable length for the interrupt,
> > and the other continuous for the timekeeping.
>
> Yes, it would certainly be interesting. 5% power savings, and no
> singing capacitors, while keeping HZ=1000. Sounds good to me.
>
> There are about 1000 timers available in PC, each having its own
> quirks. CMOS clock should be able to generate 1024Hz periodic timer
> (we currently do not use) and TSC we currently use for periodic timer
> should be usable in single-shot mode.

I guess you mean to use the CMOS clock for continuous timer, and TSC
for periodic timer?

OK, I'll take a look at it later this week or over the weekend.

Haven't looked at the x86 timer code for a while, but I think
I'll set up a new clock where we can just register a timer update
function and a periodic tick function. That way we can easily use
whatever hardware timers are available.

Tony