linux-kernel - Re: cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm)

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Date:	Fri, 01 Apr 2011 16:02:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Len Brown <lenb@...nel.org>
Cc:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>,
	arjan@...ux.intel.com, Stephen Rothwell <sfr@...b.auug.org.au>,
	suresh.b.siddha@...el.com, benh@...nel.crashing.org,
	venki@...gle.com, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com
Subject: Re: cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: cpuidle
 driver for apm)

On Fri, 2011-04-01 at 00:09 -0400, Len Brown wrote:
> > > 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:-)

Has anybody told them that pushing lots of logic into software generally
burns more amps because it keeps the thing running longer?

> 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.

Dipankar's reply seems to address this issue well.
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