On Wed, May 20, 2015 at 05:12:13PM +0800, Borislav Petkov wrote: > On Wed, May 20, 2015 at 10:55:20AM +0200, Ingo Molnar wrote: > > Does it use it to decide how 'deep' a sleep it will go into, i.e. > > larger timeouts cause longer entry and exit latencies? > > That's what the HLT thing does. Cores go into C1 and then at some point > (hysteresis, etc) the whole core complex enters C1E. > > The MWAIT* should be used for only shorter sleeps as it remains in C1. > IMHO, of course. > > But the problem there is another: what happens if the timeout fires, > you wake up and see that you can remain idle? Do HLT? Do another MWAITX > round? > > This means you have an additional unnecessary wakeup which costs. > > > I suppose it's also the case that if an interrupt arrives _before_ the > > expected timeout then MWAITX will try to exit immediately, it won't > > wait until the timeout, right? > > I'd assume so - I mean, it must, right. > > BUT!, in talking to Andy about it last night on IRC, he pointed out > that when using acpi_idle, we never come to calling x86_idle() and from > looking quickly at cpuidle_idle_call(), that still might be the case as > we go to use_default only when there's an error with the cpuidle driver > or so. > > So Rui, before you go and do more work on it, you should probably > analyze what cpuidle exactly does (if you haven't done so yet). And on > AMD we do use acpi_idle - at least on my F15h box that is the case: > > $ grep . /sys/devices/system/cpu/cpuidle/current_* > /sys/devices/system/cpu/cpuidle/current_driver:acpi_idle > /sys/devices/system/cpu/cpuidle/current_governor_ro:menu >
OK, I know. Thanks to reminder. :) Thanks, Rui -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
