On Sunday 31 October 2010 20:44:27 Alexey Fisher wrote:
> Am Sonntag, den 31.10.2010, 20:18 +0100 schrieb Andreas Mohr:
...
> >
> > Why painfully compile a custom c app to keep the CPU busy?
> >
> > Boot with processor.max_cstate=1
> > Much better performance? --> "BUG"!
> > ("BUG" == "something should probably be done about these power management
> > side
> > effects")
>
> for some reasons "processor.max_cstate=1" do not make any difference,
> cpu still use C4.
This is because the new intel_idle driver is used:
cat /sys/devices/system/cpu/cpuidle/current_driver
either you pass both:
intel_idle.max_cstate=0 processor.max_cstate=1
or with the patch I posted today to the linux-acpi list,
idle=halt (C1) idle=poll (busy idling, no power saving at all) can
be used:
[PATCH] intel_idle: Do not load if user overrides idle function via idle= boot
param
Hmm, a more generic cpuidle param:
cpuidle.max_state=
may make sense as well.
> Interesting is maxcpus=1 do difference, C4 is used and
> it perform good too.
I am not familiar with the very details of Atoms very deep
C-state implementation, but it could be that all cores/siblings
of a CPU socket need to request sleep states so that C4 or
whatever HW triggered internal power savings take place.
> So what can it be? Some SMP scheduler problem, IRQ
> balancing?
> I know intel CPUs had some PM problem, if 1 core is disabled it consume
> more power (may be no C4?).
Sounds like this is the case...
Thomas
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