From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Arve_Hj=F8nnev=E5g?= Subject: Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) Date: Wed, 2 Jun 2010 02:53:15 -0700 Message-ID: References: <201006010005.19554.rjw@sisk.pl> <20100601090023.788cabf4@notabene.brown> <201006010232.20263.rjw@sisk.pl> <20100601113309.609349fd@notabene.brown> <20100601122012.1edeaf48@notabene.brown> <20100602153235.340a7852@notabene.brown> <20100602180614.729246ea@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Thomas Gleixner Cc: Neil Brown , "Rafael J. Wysocki" , Alan Stern , Felipe Balbi , Peter Zijlstra , "Paul@smtp1.linux-foundation.org" , LKML , Florian Mickler , Linux OMAP Mailing List , Linux PM , Alan Cox , James Bottomley List-Id: linux-omap@vger.kernel.org 2010/6/2 Thomas Gleixner : > On Wed, 2 Jun 2010, Arve Hj=F8nnev=E5g wrote: >> 2010/6/2 Neil Brown : >> > There would still need to be some sort of communication between th= e the >> > suspend daemon on any event daemon to ensure that the events had b= een >> > processed. =A0This could be very light weight interaction. =A0The = point though is >> > that with this patch it becomes possible to avoid races. =A0Possib= le is better >> > than impossible. >> > >> >> We already have a solution. I don't think rejecting our solution but >> merging a worse solution should be the goal. > > That's not the goal at all. We want a solution which is acceptable fo= r > android and OTOH does not get into the way of other approaches. > I don't actually think the suspend blocker patchset get in the way of anything else. > The main problem I have is that suspend blockers are only addressing > one particular problem space of power management. > > We have more requirements than that, e.g. an active device transfer > requires to prevent the idle code to select a deep power state due to > latency requirements. > > So we then have to implement two mechanisms in the relevant drivers: > > =A0 1) telling the idle code to limit latency > =A0 2) telling the suspend code not to suspend And 3) telling the idle code to not enter low power modes that disrupt active interrupts or clocks. Our wakelock code handles 2 and 3, but I removed support for 3 on request since you can hack it by specifying a latency value that you know the low power mode cannot support. > > My main interest is to limit it to one mechanism, which is QoS based > and let idle and suspend make the appropriate decisions based on that > information. > We can use one mechanism for this, but we still have to specify both. To me this is just another naming argument and not a good reason to not merge the suspend blocker code. You have to modify the same drivers if you call suspend_block() as if you call pm_qos_update_requirement(don't suspend). We have to specify when it is not safe to suspend independent of when it is not safe to enter low power idle modes so unless you want to have a bitmap of constraints you don't save any calls. And, if we later get a constraint framework that supports everything, we can switch to it then and we will then already have some drivers annotated. --=20 Arve Hj=F8nnev=E5g