Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755489Ab3FKQp2 (ORCPT ); Tue, 11 Jun 2013 12:45:28 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:56164 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755228Ab3FKQp0 (ORCPT ); Tue, 11 Jun 2013 12:45:26 -0400 Date: Tue, 11 Jun 2013 09:45:03 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Lai Jiangshan , Linux Kernel Mailing List , Linus Torvalds , 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: <20130611164503.GI5146@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> <20130611101401.GC5146@linux.vnet.ibm.com> <1370964165.9844.172.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1370964165.9844.172.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061116-3620-0000-0000-0000030EB77A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1735 Lines: 40 On Tue, Jun 11, 2013 at 11:22:45AM -0400, Steven Rostedt wrote: > On Tue, 2013-06-11 at 03:14 -0700, Paul E. McKenney wrote: > > > > > 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 > > If the contention is with mmap_sem, then I doubt this is going to help > much, as that's a sleeping rw semaphore. Now, rw semaphores are > implemented with raw spinlocks, but I doubt that would be the main point > of contention, compared to the sleeping part. If I remember correctly, someone actually hit this earlier this year, which prompted use of a special-purpose queued lock to guard the semaphore data. I don't recall whether it was mmap_sem or not, so cannot say whether it was a straight mutex or an rw semaphore. Thanx, Paul > -- Steve > > > 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: > > > > -- 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/