linux-kernel - Re: [PATCH 5/6] intel_idle: Add ->enter

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Message-ID: <2502414.MyBzvuWGMR@vostro.rjw.lan>
Date:	Thu, 05 Mar 2015 01:18:38 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	John Stultz <john.stultz@...aro.org>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 5/6] intel_idle: Add ->enter_freeze callbacks

On Thursday, March 05, 2015 07:50:26 AM Li, Aubrey wrote:
> On 2015/2/13 0:24, Rafael J. Wysocki wrote:
> > On Thursday, February 12, 2015 02:26:43 PM Peter Zijlstra wrote:
> >>
> >> Why bother with enter_freeze() for any but the deepest state (C6 in this
> >> case)?
> > 
> > User space may disable the deepest one (and any of them in general) via sysfs
> > and there's no good reason to ignore its choice in this particular case while
> > we're honoring it otherwise.
> > 
> > So the logic is basically "find the deepest one which isn't disabled" and
> > setting the pointers costs us nothing really.
> > 
> 
> If the user has chance to disable C6 via /sys, that means c6 works?
> Shouldn't we ignore user space setting during freeze? Otherwise, we will
> lost S0ix?

We can't ignore it, because we don't know the reason why the state was
disabled.

It may just not work reliably enough on the given platform.


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