Messages in this thread | | | Date | Fri, 16 May 2008 10:40:59 +0200 | From | Ingo Molnar <> | Subject | Re: [BISECTED] Lots of "rescheduling IPIs" in powertop |
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* Andreas Herrmann <andreas.herrmann3@amd.com> wrote:
> > > Recap: powertop shows between 200-400 wakeups/second with the > > > description "<kernel IPI>: Rescheduling interrupts" when all > > > processors have load (e.g. I need to run two busy-loops on my > > > 2-CPU system for this to show up). > > > > ok, could you try the fix below? It was a mistake to make mwait use > > dependent on power considerations - on a desktop CPU it is unlikely > > to use more power than a simple HLT - and the IPIs are extra > > scheduling latency and extra power used. > > It depends on the CPU. For AMD CPUs that support MWAIT this is wrong. > Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings then > depend on a clock divisor and current Pstate of the core. > > If all cores of a processor are in halt state (C1) the processor can > enter the C1E (C1 enhanced) state. If mwait is used this will never > happen. > > Thus HLT saves more power than MWAIT here. > > It might be best to switch off the mwait flag for these AMD CPU > families like it was introduced with commit > f039b754714a422959027cb18bb33760eb8153f0 (x86: Don't use MWAIT on AMD > Family 10)
agreed, that looks like the cleanest solution. Could you please send a patch for that, ontop of my patch?
Ingo
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