Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754210AbaBFDJF (ORCPT ); Wed, 5 Feb 2014 22:09:05 -0500 Received: from g6t0185.atlanta.hp.com ([15.193.32.62]:20116 "EHLO g6t0185.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750952AbaBFDJE (ORCPT ); Wed, 5 Feb 2014 22:09:04 -0500 Message-ID: <52F2FCB3.7090400@hp.com> Date: Wed, 05 Feb 2014 22:08:35 -0500 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Ingo Molnar CC: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Andrew Morton , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , Linus Torvalds , Raghavendra K T , George Spelvin , Tim Chen , aswin@hp.com, Scott J Norton Subject: Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation References: <1390537731-45996-1-git-send-email-Waiman.Long@hp.com> <20140130130453.GB2936@laptop.programming.kicks-ass.net> <20140130151715.GA5126@laptop.programming.kicks-ass.net> <20140131092616.GC5126@laptop.programming.kicks-ass.net> <52EBF276.1020505@hp.com> <20140131201401.GD2936@laptop.programming.kicks-ass.net> <52EC110D.4030509@hp.com> <20140202090357.GA1006@gmail.com> In-Reply-To: <20140202090357.GA1006@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/02/2014 04:03 AM, Ingo Molnar wrote: > * Waiman Long wrote: > >> How about making the selection of MCS or ticket queuing either user >> configurable or depending on the setting of NR_CPUS, NUMA, etc? > No! > > There are lots of disadvantages to adding such CONFIG_NUMA Kconfig > variants for locking primitives: > > - an doubling of the test matrix > > - an doubling of the review matrix and a halving of effective review > capacity: we've just about go the capacity to review and validate > patches like this. Splitting out a 'only NUMA cares' variant is a > non-starter really. > > - but most importantly, there's absolutely no reason to not be fast > on 128 CPU systems in the low contended case either! Sacrificing > the low contended case with 'on 128 CPU systems it is the contended > path that matters' is an idiotic argument. > > Essentially the only area were we allow Kconfig dependencies are > unyielding physical forces: such as lots of CPUs needing a wider CPU > mask. > > As Peter said it, the right solution is to fix the contended case. If > that also happens to speed up or better organize the uncondended code > then that's good, but it should not make it worse. > > Thanks, > > Ingo You are right. I am trying to measure the performance impact of MCS queuing has on a lightly contended system. I need to write some custom test code to get that information. With that information, I may be able to tune it to perform more or less on par with ticket lock. As for the additional cache line access of the MCS lock, I don't think it is really an issued as the MCS node is allocated on local stack which is likely to be in the cache anyway. I will report back when I have more data. -Longman -- 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/