On Friday 14 May 2010, Tony Lindgren wrote: > * Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> [100513 14:56]: > > On Thu, 13 May 2010, Tony Lindgren wrote: > > > > > > > And that's why > > > > > it should be handled by runtime power management instead. > > > > > > > > Runtime PM is not capable of freezing userspace and shutting down CPUs. > > > > More or less by definition -- if it could then it wouldn't be "runtime" > > > > any more, since the processor wouldn't be running. > > > > > > Not true. We are already powering off CPUs and rebooting them for > > > at least omaps in every idle loop using cpuidle. The memory stays on. > > > > Okay, that's a valid point. But is that approach usable in general > > (i.e., on non-OMAP systems)? > > Yes if your system wakes to interrupts at least. If your system does > not wake to timer events, then you'll get missed timers. So it should > work on PC too with CONFIG_NO_HZ and if RTC was used for the timer > wake event. > > > How do you handle situations where the CPU is currently idle but an > > event (such as I/O completion) is expected to occur in the near future? > > You don't want to power-off and reboot then, do you? > > The idle code looks at next_timer_interrupt() value, then if the > next timer event if far enough ahead, the system powers down and > wakes to the timer interrupt. It also wakes to device interrupts. For the record, waking to interrupts doesn't work on quite some systems (like ACPI-based PCs for one example). Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
