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

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Message-ID: <1675732.Zj8pe2mRTV@vostro.rjw.lan>
Date:	Tue, 13 May 2014 01:53:49 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	"Li, Aubrey" <aubrey.li@...ux.intel.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	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 Monday, May 12, 2014 04:52:22 PM Daniel Lezcano wrote:
> On 05/12/2014 04:19 PM, Li, Aubrey wrote:
> > 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.
> 
> Ok, let me rephrase it. Why not revisiting cpuidle_play_dead instead ?

Many drivers don't implement the ->enter_dead() callback.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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