* Zwane Mwaikambo <[EMAIL PROTECTED]> [050809 07:17]: > On Mon, 8 Aug 2005, Tony Lindgren wrote: > > > As far as I remember enabling AMD stop grant disconnects all cpus. This > > means the system won't be able to do any work until the dyntick timer > > interrupt wakes up the system. > > > > > Both requirements (idling all CPUs together vs individually) I think > > > will make the patch more complex. Are such systems (which require having > > > to > > > idle all CPUs together) pretty common that we have to care about?! > > > > Probably all AMD SMP based systems? Somebody with better knowledge should > > verify this. > > It would be the K7 only.
OK, still quite a few systems. > > > But that may be too late on some CPUs. If dyn_tick->skip = 100, all > > > CPUs skip 100 ticks. However some CPUs may have timers that need to be > > > service much before that. > > > > Not in the current case, as the system is completely idle until some > > interrupt wakes up the system. Of course it would be different if you make > > it per-CPU. > > I once did a weekend version of this with SMP support and for the PIT, i > had the last cpu to enter idle turn reprogram the PIT. Unfortunately this > means waiting for all processors and isn't as effective as a result. > > > Well we need to be able to do various things in the idle loop depending on > > the length of the estimated sleep. For example, if next_timer_interrupt is > > 2 jiffies away, we cannot do much. But if next_timer_interrupt is 2 seconds > > away, we can idle pretty much all devices. > > > > > > But in any case on P4 systems the APIC timer is not the bottleneck as > > > > stopping or reprogramming PIT also kills APIC. (This does not happen on > > > > P3 > > > > systems). So the bottleneck most likely is the length of PIT. > > > > > > On these systems, do you disabled APIC (dyntick=noapic)? > > > > Yeah. It only seems to work on P3 systems. > > Odd, does reprogramming the APIC at that point get it going again? Hmmm, might be worth trying. Tony - 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/