Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754527Ab3FKKOM (ORCPT ); Tue, 11 Jun 2013 06:14:12 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:53809 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752478Ab3FKKOK (ORCPT ); Tue, 11 Jun 2013 06:14:10 -0400 Date: Tue, 11 Jun 2013 03:14:01 -0700 From: "Paul E. McKenney" To: Lai Jiangshan Cc: Linux Kernel Mailing List , Linus Torvalds , Steven Rostedt , Ingo Molnar , Dipankar Sarma , Andrew Morton , Mathieu Desnoyers , Josh Triplett , niv@us.ibm.com, Thomas Gleixner , Peter Zijlstra , Valdis Kletnieks , David Howells , Eric Dumazet , Darren Hart , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , sbw@mit.edu Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock Message-ID: <20130611101401.GC5146@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20130609193657.GA13392@linux.vnet.ibm.com> <1370911480.9844.160.camel@gandalf.local.home> <51B6D76D.9090207@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51B6D76D.9090207@cn.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061110-4834-0000-0000-000007F213AC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2579 Lines: 57 On Tue, Jun 11, 2013 at 03:53:17PM +0800, Lai Jiangshan wrote: > On 06/11/2013 08:51 AM, Linus Torvalds wrote: > > On Mon, Jun 10, 2013 at 5:44 PM, Steven Rostedt wrote: > >> > >> OK, I haven't found a issue here yet, but youss are beiing trickssy! We > >> don't like trickssy, and we must find precccciouss!!! > > > > .. and I personally have my usual reservations. I absolutely hate > > papering over scalability issues, and historically whenever people > > have ever thought that we want complex spinlocks, the problem has > > always been that the locking sucks. > > > > So reinforced by previous events, I really feel that code that needs > > this kind of spinlock is broken and needs to be fixed, rather than > > actually introduce tricky spinlocks. > > > > So in order to merge something like this, I want (a) numbers for real > > loads and (b) explanations for why the spinlock users cannot be fixed. > > > > Because "we might hit loads" is just not good enough. I would counter > > with "hiding problems causes more of them". > > > > Hi, all > > Off-topic, although I am in this community for several years, > I am not exactly clear with this problem. > > 1) In general case, which lock is the most competitive in the kernel? what it protects for? > 2) In which special case, which lock is the most competitive in the kernel? what it protects for? > 3) In general case, which list is the most hot list? > 4) In which special case, which list is the most hot list? Others would know better than I, but mmap_sem has been called out as a prime offender for some workloads. There is of course some debate as to whether the fault lies mmap_sem or with the workloads. There have been some efforts to solve this one on LKML, plus some in academia have worked on this as well: http://people.csail.mit.edu/nickolai/papers/clements-bonsai.pdf http://pdos.csail.mit.edu/papers/radixvm:eurosys13.pdf And IIRC this was the subject of a session at a recent minisummit. There are a few locks within the RCU implementation that have popped up from time to time on very large systems, but I have dealt with those and have plans for each should it become a problem. The plans probably won't survive first contact with a real workload, but having thought things through is very helpful. Thanx, Paul -- 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/