From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [RFC 2/4] ARM: OMAP: PM: Get rid of Powerdomain book-keeping from cpuidle Date: Thu, 26 Jul 2012 10:44:25 -0700 Message-ID: <87boj2s9hi.fsf@ti.com> References: <1342764284-8143-1-git-send-email-rnayak@ti.com> <1342764284-8143-3-git-send-email-rnayak@ti.com> <5009120A.1060400@ti.com> <1342774283.4672.181.camel@sokoban> <87obn3798o.fsf@ti.com> <50113B3C.4090608@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from na3sys009aog111.obsmtp.com ([74.125.149.205]:40510 "EHLO na3sys009aog111.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752218Ab2GZRo0 (ORCPT ); Thu, 26 Jul 2012 13:44:26 -0400 Received: by pbcwy7 with SMTP id wy7so4296589pbc.17 for ; Thu, 26 Jul 2012 10:44:24 -0700 (PDT) In-Reply-To: <50113B3C.4090608@ti.com> (Rajendra Nayak's message of "Thu, 26 Jul 2012 18:12:36 +0530") Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Rajendra Nayak Cc: t-kristo@ti.com, "Shilimkar, Santosh" , linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, paul@pwsan.com, b-cousson@ti.com Rajendra Nayak writes: > On Thursday 26 July 2012 04:13 AM, Kevin Hilman wrote: >> Tero Kristo writes: >> >>> On Fri, 2012-07-20 at 13:38 +0530, Rajendra Nayak wrote: >>>> On Friday 20 July 2012 12:55 PM, Shilimkar, Santosh wrote: >>>>> On Fri, Jul 20, 2012 at 11:34 AM, Rajendra Nayak wrote: >>>>>> pwrdm_pre_transition()/pwrdm_post_transition() have always been high latency >>>>>> operations done within cpuidle to do Powerdomain level book-keeping to know >>>>>> what state transitions for different Powerdomains have been triggered. >>>>>> This is also useful to do a restore-on-demand in some cases when we know >>>>>> the context for the given Powerdomain was lost etc. >>>>>> >>>>>> Now that we have definitive entry/exit points (thanks to the Powerdomain >>>>>> level usecounting) for Powerdomain transitions, these book-keeping functions >>>>>> can very well be moved from within CPUidle into pwrdm_clkdm_enable()/pwrdm_ >>>>>> clkdm_disable() functions. >>>>>> >>>>>> Also rename _pwrdm_pre/post_transition_cb() to pwrdm_pre/post_transition() >>>>>> and get rid of the original ones which iterate over all powerdomains. >>>>>> >>>>>> Signed-off-by: Rajendra Nayak >> >> This is excellent! Thanks for working on this. >> >> However, it needs a rebase against mainline though because I merged a >> set of optimizations[1] to this code already that only calls pre/post >> per-pwrdm. >> > > Hi Kevin, > > I thought some more on this patch, and I think this way of collecting > stats and knowing what state transitions the powerdomains been through > will not work on OMAP3, mainly because of the autodeps. Might work on > OMAP4 and beyond which do not need any autodeps. > > Here why I think so, > Lets assume a Powerdomain X with a last module Y active, once Y disables > the last clock (lets assume no hardware controlled clocks for > simplicity), we clear the last power state register for X. However > due to autodeps X does not transition to a target state immediately. > It only does so when the MPU (and IVA) go down, and because > of the wakeup dependency (autodeps set a sleep and a wakeup dep with > both MPU and IVA) is also woken up every time MPU or IVA are up. > So its quite possible that X transitions in and out of sleep multiple > times before Y decides to re-enable its clocks, which is when we end up > looking for the last power state entered. > Lets say X entered OFF 3 times in between Y disabling and re-enabling > its clocks. Though we end up updating the counter only once (instead of > 3) we still know and can tell Y that it lost context. > The problem however arises if for some reason X entered OFF > twice and happened to stay ON the third time the dependencies were met. > When Y re-enables its clocks, we end up telling it that it *did not* > lose context because we see the previous power state was ON. Yeah, this is definitely a problem. As long as we have autodeps, everything is centralized around CPU transitions anyways, so it makes sense to keep the accounting centralized too. > I think as long as we have autodeps, the only way on OMAP3 to accurately > do this is to do it for all dependent domains in CPUIdle :( Or, to get rid of autodeps. ;) Kevin