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[Xen-devel] Re: cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: c

To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm)
From: Len Brown <lenb@xxxxxxxxxx>
Date: Fri, 01 Apr 2011 00:09:25 -0400 (EDT)
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>, ak@xxxxxxxxxxxxxxx, suresh.b.siddha@xxxxxxxxx, venki@xxxxxxxxxx, benh@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx>, arjan@xxxxxxxxxxxxxxx, Trinabh Gupta <trinabh@xxxxxxxxxxxxxxxxxx>
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> > Moorestown is already an example of an asymmetric system,
> > since its deepest c-state is available on cpu0, but not on cpu1.
> > So it needs different tables for each cpu. 
> 
> wtf are these hardware guys smoking and how the heck are we supposed to
> schedule on such a machine? Prefer to keep cpu1 busy while idling cpu0?

they are smoking micro-amps:-)

S0i3 on cpu0 can be entered only after cpu1 is already off-line,
among other system hardware dependencies...

So it makes no sense to export S0i3 as a c-state on cpu1.

When cpu1 is online, the scheduler treats it as a normal SMP.

cheers,
-Len Brown, Intel Open Source Technology Center



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