Messages in this thread | | | Date | Tue, 14 Dec 2004 15:13:00 -0800 | From | Tony Lindgren <> | Subject | Re: dynamic-hz |
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* linux-os <linux-os@chaos.analogic.com> [041214 15:04]: > On Tue, 14 Dec 2004, Pavel Machek wrote: > > >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. > > Pavel > >-- > > If you use that RTC timer, it needs to be something that can be > turned OFF. Many embedded applications use that because its the > only timer that the OS doesn't muck with. It also has very low > noise which makes in a good timing source for IIR filters for > high precision, low data-rate data acquisition (like 24 bits).
OK, thanks for the information. That could be the continuous timer then, and TSC the periodic timer.
> Since it generates an edge, its interrupt can't be shared. > I certainly hope that you don't use it. One can read the > time without disturbing the interrupt rate. One just > needs to use the existing rtc_lock and not spin with > the lock being held.
Yeah, the timer update would be just a read from the RTC timer.
> Currently the kernel RTC software allocates the RTC interrupt > even though it doesn't use it. This makes it necessary to > compile the RTC as a module and then remove it when another > driver needs to use the RTC interrupt source.
The interrupt could be used for timer wrap only.
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