linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

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Message-ID: <AANLkTinwJdPneNSlAeTml5fHW2LFy53Dz3DRf95y1Bcl@mail.gmail.com>
Date:	Fri, 14 May 2010 20:40:08 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Kevin Hilman <khilman@...prootsystems.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Tony Lindgren <tony@...mide.com>,
	Matthew Garrett <mjg@...hat.com>,
	Paul Walmsley <paul@...an.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	magnus.damm@...il.com, "Theodore Ts'o" <tytso@....edu>,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>,
	Benoît Cousson <b-cousson@...com>,
	linux-omap@...r.kernel.org, Vitaly Wool <vitalywool@...il.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

On Fri, May 14, 2010 at 7:58 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Fri, 14 May 2010, Brian Swetland wrote:
>
>> It provides useful functionality -- you apparently disagree, but the
>> wakelock/suspendblock model is in use, shipping, and solving problems
>> for quite a lot of android devices that have been shipping for a while
>> now.  We actively go to lowest power state in idle (on omap, msm,
>> etc), and use drivers that aggressively declock and depower modules
>> (similar to runtime pm), but we have found that using the
>> opportunistic suspend model combined with wakelocks allows us to
>> attain even lower average power consumption in always-connected,
>> actively-syncing devices.
>
> Can you explain this in more detail?  Are you saying that some devices
> go on generating interrupts and causing timers to be scheduled, even
> though what they're doing isn't important enough to prevent the system
> from powering down?

In tickless mode, the time until next timer is a signed int, so the
longest the kernel will ever sleep is ~2 seconds at a go.  In
practice, userspace entities often have polling behavior that can
trigger more often than that, and I've observed some kernel periodic
timers (haven't cataloged them recently) that happen more often than
once a second.

When we go to full suspend, we know that only specific wakeup sources
(keyboard gpios, baseband voice/ip events, rtc alarms, etc) are going
to wake us up.

Brian
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