From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 9487B273 for ; Tue, 28 Jul 2015 22:04:19 +0000 (UTC) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id C0B8F7C for ; Tue, 28 Jul 2015 22:04:17 +0000 (UTC) Date: Wed, 29 Jul 2015 08:03:50 +1000 From: NeilBrown To: "Rafael J. Wysocki" Message-ID: <20150729080350.17f9f96a@noble> In-Reply-To: <8734973.3SWuCLvkiU@vostro.rjw.lan> References: <20150723105726.GC30929@amd> <20150724143427.5a045528@noble> <20150724060049.GX10928@atomide.com> <8734973.3SWuCLvkiU@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Bjorn Andersson , ksummit-discuss@lists.linuxfoundation.org, riverful.kim@samsung.com, kyungmin.park@samsung.com, John Stultz , Pavel Machek Subject: Re: [Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 25 Jul 2015 00:26:03 +0200 "Rafael J. Wysocki" wrote: > On Thursday, July 23, 2015 11:00:49 PM Tony Lindgren wrote: > > * NeilBrown [150723 21:37]: > > > On Thu, 23 Jul 2015 22:34:29 +0200 Pavel Machek wrote: > > > > > > > > and the big one... for Android people (not me): > > > > > > > > 6) do we need to use s2ram (and then pretend phone is not suspended) > > > > to save power on cellphones? If so, do we need new interface for > > > > applications to signal "I'd really like to run"? > > > > > > > > > > For the first half of this question, the answer is: > > > Probably not. runtime-pm should be able to put all devices to sleep, > > > and cgroup freezer should be able to freeze untrusted processes. > > > > Yes s2ram is just an additional tool. PM runtime alone can > > already provide a reasonable battery life for a phone as long as > > it's properly implemented and the hardware supports it. With > > reasonable battery life in this case I mean over 10 days in idle > > mode with system running and timers working. > > > > > But I suspect runtime-pm doesn't provide as much power saving as > > > system suspend, and using the cgroup freezer means lots of changes to > > > userspace. > > > So lots of work would be needed to meet this goal, if it is a > > > worthwhile goal. > > > > And with s2ram the difference is that then the system is not running > > and timers don't work so it really needs to be optional. > > Right. > > Even with suspend-to-idle we can get less energy usage with respect to > runtime idle (device runtime PM plus cpuidle) just because timer events > are disabled then. > Is this just the timer interrupt which keeps the clock up to date, or are there other timer events which keep ticking? Would it be possible for the wall-clock timer to stop if the system has been idle for a while, and for the RTC to be used to recover the correct time when activity restarts? Thanks, NeilBrown