On Fri, Jul 15, 2005 at 07:02:24PM +0200, Andi Kleen wrote: > > At least on multi processor systems LAPIC has to work anyways (otherwise > you cannot schedule other CPUs), so it is fine to use there. > > AFAIK there are no x86 CPUs right now that do both C3 > and SMP. If they ever do then they will need to keep the > LAPIC ticking in C3. > > This has nothing even to do with advanced power saving, > but is pretty much a hard requirement for Linux (and I would > be surprise if it wasn't one for other OS too). Without it > scheduling and local timers on APs will not work at all. > > In theory it could be replaced with HPET if HPET had enough banks (one > for each CPU - most implementations today usually only have 2 or 4), but > that would severly limit scalability for lazy tick schemes because > they would depend on a common resource in the southbridge. Also the > max number of banks needed on a big system would be huge > (128? 256?) because you couldn't have more CPUs than that. > > With PIC only it's absolutely impossible. >
I wouldn't say it is totally impossible. There are ways in which Linux can work without a reliable Local APIC timer. One option being - make one CPU that gets the external timer interrupt multicast an IPI to all the other CPUs that wants to get periodic timer interrupt. Thanks, Venki - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
