linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <20100601135102.GA8098@srcf.ucam.org>
Date:	Tue, 1 Jun 2010 14:51:02 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	tytso@....edu, LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	felipe.balbi@...ia.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Mon, May 31, 2010 at 04:21:09PM -0500, James Bottomley wrote:

> You're the one mentioning x86, not me.  I already explained that some
> MSM hardware (the G1 for example) has lower power consumption in S3
> (which I'm using as an ACPI shorthand for suspend to ram) than any
> suspend from idle C state.  The fact that current x86 hardware has the
> same problem may be true, but it's not entirely relevant.

As long as you can set a wakeup timer, an S state is just a C state with 
side effects. The significant one is that entering an S state stops the 
process scheduler and any in-kernel timers. I don't think Google care at 
all about whether suspend is entered through an explicit transition or 
something hooked into cpuidle - the relevant issue is that they want to 
be able to express a set of constraints that lets them control whether 
or not the scheduler keeps on scheduling, and which doesn't let them 
lose wakeup events in the process.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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