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

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Message-ID: <1900403.uK8ecXs4pj@vostro.rjw.lan>
Date:	Fri, 09 May 2014 23:25:33 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.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 Friday, May 09, 2014 04:13:56 PM Pavel Machek wrote:
> On Fri 2014-05-09 13:26:47, Rafael J. Wysocki wrote:
> > On Friday, May 09, 2014 09:38:35 AM Pavel Machek wrote:
> > > On Mon 2014-05-05 00:51:54, 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.
> > > 
> > > Would there be way to pass the parameter "go to deepest" instead of adding
> > > global state for this?
> > 
> > I'm not sure what you mean?  A parameter of what in particular?  And where
> > to pass it?
> 
> Currently the code is:
> 
> static void freeze_enter(void)
> {
> + cpuidle_use_deepest_state(true);
>   cpuidle_resume();
>   wait_event(suspend_freeze_wait_head, suspend_freeze_wake);
>   cpuidle_pause();
> + cpuidle_use_deepest_state(false);
> }
> 
> . I believe it would be better if you did
> 
> cpuidle_resume(GOTO_DEEPEST_C_STATE)
> 
> instead of having global state.

That's a good idea actually.  I'll do that on top of the $subject patch.

Thanks!

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