From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754398AbZLWInx (ORCPT ); Wed, 23 Dec 2009 03:43:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752333AbZLWInw (ORCPT ); Wed, 23 Dec 2009 03:43:52 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:52150 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752017AbZLWInv (ORCPT ); Wed, 23 Dec 2009 03:43:51 -0500 Date: Wed, 23 Dec 2009 09:42:53 +0100 From: Ingo Molnar To: Tejun Heo Cc: Linus Torvalds , Peter Zijlstra , awalls@radix.net, linux-kernel@vger.kernel.org, jeff@garzik.org, akpm@linux-foundation.org, jens.axboe@oracle.com, rusty@rustcorp.com.au, cl@linux-foundation.org, dhowells@redhat.com, arjan@linux.intel.com, avi@redhat.com, johannes@sipsolutions.net, andi@firstfloor.org Subject: Re: workqueue thing Message-ID: <20091223084253.GB25240@elte.hu> References: <1261405604.4314.154.camel@laptop> <4B3009DC.7020407@kernel.org> <1261480001.4937.21.camel@laptop> <4B319A20.9010305@kernel.org> <20091223060229.GA14805@elte.hu> <4B31C210.4010100@kernel.org> <20091223080144.GG23839@elte.hu> <20091223081238.GA29963@elte.hu> <4B31D5A7.2040608@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B31D5A7.2040608@kernel.org> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=none autolearn=no SpamAssassin version=3.2.5 _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Tejun Heo wrote: > Hello, Ingo. > > On 12/23/2009 05:12 PM, Ingo Molnar wrote: > > > > * Ingo Molnar wrote: > > > >> At least as far as i'm concerned, i'd like to see actual uses. It's a big > >> linecount increase all things considered: > >> > >> 20 files changed, 2783 insertions(+), 660 deletions(-) > > BTW, the code contains way more comment afterwards and has other benefits > like not having crazy number of workers around on many core machines. (the original workqueue.c had way more comments as well.) > >> and you say it _wont_ help performance/scalability (this aspect wasnt clear > > And I think it will help scalability for sure although it depends on > what type of scalability you're talking about. _I_ am not making any claims - i am simply asking what the benefits are, just to move the discussion forward. If there are benefits, it must be measurable, simple as that. > >> to me from previous discussions), so the (yet to be seen) complexity > >> reduction in other code ought to be worth it. > > > > To further stress this point, i'd like to point to the very first commit that > > introduced kernel/workqueue.c into Linux 7 years ago: > > > > | From 6ed12ff83c765aeda7d38d3bf9df7d46d24bfb11 Mon Sep 17 00:00:00 2001 > > | From: Ingo Molnar > > | Date: Mon, 30 Sep 2002 22:17:42 -0700 > > | Subject: [PATCH] [PATCH] Workqueue Abstraction > > > > look at the diffstat of that commit: > > > > 201 files changed, 1102 insertions(+), 1194 deletions(-) > > > > despite adding a new abstraction and kernel subsystem (workqueues), that > > commit modified more than a hundred drivers to make use of it, and managed to > > achieve a net linecount decrease of 92 lines - despite adding hundreds of > > lines of a new core facility. > > > > Likewise, for this particular patchset it should be possible to identify > > existing patterns of code in the existing code base of 6+ millions lines of > > Linux driver code that would make the advantages of this +2000 lines of core > > kernel code plain obvious. There were multipe claims of problems with the > > current abstractions - so there sure must be a way to show off the new code in > > I'm not sure I'm gonna update that many places in a single sweep but yeah > let's give it a shot. In all fairness the original workqueue.c had an advantage, that it basically piggybacked on usable patterns from the tqueue (task-queue) abstraction - and that was rather repetitive. Your code adds a new _paradigm_ for which no easily reusable patterns exist - so under no way are you expected to show such a massive amount of conversion - just a handful of cases would be enough to show the benefits - we can extrapolate from there. It would also give us hands-on experience with the utility (and robustness) of your proposal, so it's a win-win proposal IMO. Thanks, Ingo