linux-kernel - Re: [PATCH] PM / suspend: Always use deepest C-state in the "freeze" sleep state

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Message-ID: <5370D85C.3090505@linux.intel.com>
Date:	Mon, 12 May 2014 22:19:08 +0800
From:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Aubrey Li <aubrey.li@...el.com>
Subject: Re: [PATCH] PM / suspend: Always use deepest C-state in the "freeze"
 sleep state

On 2014/5/12 22:08, Daniel Lezcano wrote:
> On 05/05/2014 12:51 AM, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> If freeze_enter() is called, we want to bypass the current cpuidle
>> governor and always use the deepest available (that is, not disabled)
>> C-state, because we want to save as much energy as reasonably possible
>> then and runtime latency constraints don't matter at that point, since
>> the system is in a sleep state anyway.
>>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> ---
>>
>> This is on top of https://patchwork.kernel.org/patch/4071541/ .
>>
> 
> Wouldn't make sense to revisit play_dead instead ?
> 
play_dead() is broken.

Even if it works, we still should rely on cpuidle driver to place the
CPUs into the deepest c-state, because there is no architectural way to
enter deepest c-state and what play_dead() does is a bad assumption.

Thanks,
-Aubrey

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