linux-kernel - Re: [PATCH v9 2/4] cpuidle: Remove CPUIDLE_FLAG

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Message-ID: <4EAABB07.3000305@linux.intel.com>
Date:	Fri, 28 Oct 2011 07:24:07 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
CC:	khilman@...com, venki@...gle.com, ak@...ux.intel.com,
	len.brown@...el.com, peterz@...radead.org, rjw@...k.pl,
	santosh.shilimkar@...com, lenb@...nel.org,
	linux-pm@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 2/4] cpuidle: Remove CPUIDLE_FLAG_IGNORE and dev->prepare()


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On 10/28/2011 3:50 AM, Deepthi Dharwar wrote:
> The cpuidle_device->prepare() mechanism causes updates to the
> cpuidle_state[].flags, setting and clearing CPUIDLE_FLAG_IGNORE
> to tell the governor not to chose a state on a per-cpu basis at
> run-time. State demotion is now handled by the driver and it returns
> the actual state entered. Hence, this mechanism is not required.
> Also this removes per-cpu flags from cpuidle_state enabling
> it to be made global.
>
 
having worked on some newer platforms....
this one is really still needed. doing this inside the actual states
does not work,
because if the deepest 3 states are invalid, the same (somewhat
expensive) test would have to be done 3 times,
and each of the states would have to fail before the 4th one gets chosen.
that's just not going to work
 
(in the state handler you can't know what other state to fall back to,
and especially not how to enter such a fallback state)
 
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