Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932373Ab0FDOYE (ORCPT ); Fri, 4 Jun 2010 10:24:04 -0400 Received: from cantor2.suse.de ([195.135.220.15]:52821 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932153Ab0FDOYB (ORCPT ); Fri, 4 Jun 2010 10:24:01 -0400 Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) From: James Bottomley To: Arve =?ISO-8859-1?Q?Hj=F8nnev=E5g?= Cc: "Rafael J. Wysocki" , markgross@thegnar.org, 640e9920@gmail.com, Peter Zijlstra , Brian Swetland , Ingo Molnar , LKML , Florian Mickler , Linux PM , Thomas Gleixner , Alan Cox In-Reply-To: References: <1275575794.5914.74.camel@mulgrave.site> <201006032305.58082.rjw@sisk.pl> Content-Type: text/plain; charset="UTF-8" Date: Fri, 04 Jun 2010 09:23:10 -0500 Message-ID: <1275661390.4455.31.camel@mulgrave.site> Mime-Version: 1.0 X-Mailer: Evolution 2.28.2 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4714 Lines: 104 On Thu, 2010-06-03 at 21:07 -0700, Arve Hjønnevåg wrote: > On Thu, Jun 3, 2010 at 2:05 PM, Rafael J. Wysocki wrote: > > On Thursday 03 June 2010, James Bottomley wrote: > >> On Thu, 2010-06-03 at 00:10 -0700, Arve Hjønnevåg wrote: > >> > On Wed, Jun 2, 2010 at 10:40 PM, mark gross <640e9920@gmail.com> wrote: > >> > > On Wed, Jun 02, 2010 at 09:54:15PM -0700, Brian Swetland wrote: > >> > >> On Wed, Jun 2, 2010 at 8:18 PM, mark gross <640e9920@gmail.com> wrote: > >> > >> > On Wed, Jun 02, 2010 at 02:58:30PM -0700, Arve Hjønnevåg wrote: > >> > >> >> > >> > >> >> The list is not short. You have all the inactive and active > >> > >> >> constraints on the same list. If you change it to a two level list > >> > >> >> though, the list of unique values (which is the list you have to walk) > >> > >> >> may be short enough for a tree to be overkill. > >> > >> > > >> > >> > what have you seen in practice from the wake-lock stats? > >> > >> > > >> > >> > I'm having a hard time seeing where you could get more than just a > >> > >> > handfull. However; one could go to a dual list (like the scheduler) and > >> > >> > move inactive nodes from an active to inactive list, or we could simply > >> > >> > remove them from the list uppon inactivity. which would would well > >> > >> > after I change the api to have the client allocate the memory for the > >> > >> > nodes... BUT, if your moving things in and out of a list a lot, I'm not > >> > >> > sure the break even point where changing the structure helps. > >> > >> > > >> > >> > We'll need to try it. > >> > >> > > >> > >> > I think we will almost never see more than 10 list elements. > >> > >> > > >> > >> > --mgross > >> > >> > > >> > >> > > >> > >> > >> > >> I see about 80 (based on the batteryinfo dump) on my Nexus One > >> > >> (QSD8250, Android Froyo): > >> > > > >> > > shucks. > >> > > > >> > > well I think for a pm_qos class that has boolean dynamic range we can > >> > > get away with not walking the list on every request update. we can use > >> > > a counter, and the list will be for mostly for stats. > >> > > > >> > > >> > Did you give any thought to my suggestion to only use one entry per > >> > unique value on the first level list and then use secondary lists of > >> > identical values. That way if you only have two constraints values the > >> > list you have to walk when updating a request will never have more > >> > than two entries regardless of how many total request you have. > >> > > >> > A request update then becomes something like this: > >> > if on primary list { > >> > unlink from primary list > >> > if secondary list is not empty > >> > get next secondary entry and add in same spot on primary list > >> > } > >> > unlink from secondary list > >> > find new spot on primary list > >> > if already there > >> > add to secondary list > >> > else > >> > add to primary list > >> > >> This is just reinventing hash bucketed lists. To get the benefits, all > >> we do is implement an N state constraint as backed by an N bucketed hash > >> list, which the kernel already has all the internal mechanics for. > > > > Agreed. > > > > No, a hash is used for quick lookup of a specific value, not to find > an extreme value. If you only have N possible values an N bucket hash list is rather efficient (provided N is small). But I would agree that knowing what N is represents an API change, and since plists can do this without changing the API, they're better. > It is however extremely similar to plists. The only > difference is that plists link all the secondary lists together. Right, so they would solve the *current* problem exactly. > If we > want to have constraints that autoexpire, then keeping the secondary > lists separate allows the same optimization as I did for > wakelock/suspend_blocker timeouts where no timer is active if an > (equal or stricter) non-expiring constraint is active. But this is a future discussion and not part of the patch. The way open source works is that we sort out the best implementation for the current conditions. If the implementation has to change because of future stuff, then we change it when the future stuff comes along. Changing implementations is easy (they don't have any externally visible impact). Changing the in-kernel API is slightly harder, but easily doable. It's only changing the user visible ABI that we worry about and try not to do. James -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/