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

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Message-ID: <4D95E35F.2080707@linux.intel.com>
Date:	Fri, 01 Apr 2011 07:38:23 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	dipankar@...ibm.com
CC:	Len Brown <lenb@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Trinabh Gupta <trinabh@...ux.vnet.ibm.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 4/1/2011 1:15 AM, Dipankar Sarma wrote:
> On Fri, Apr 01, 2011 at 12:09:25AM -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:-)
>>
>> 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.
> Isn't S0i3 a "system" state, as opposed to cpu state ?

it's misnamed. it's a C state to the OS.


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