Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756741Ab3H3P2g (ORCPT ); Fri, 30 Aug 2013 11:28:36 -0400 Received: from mail-ve0-f180.google.com ([209.85.128.180]:44095 "EHLO mail-ve0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756121Ab3H3P2e (ORCPT ); Fri, 30 Aug 2013 11:28:34 -0400 MIME-Version: 1.0 In-Reply-To: <20130830071612.GB14099@gmail.com> References: <1375758759-29629-1-git-send-email-Waiman.Long@hp.com> <1375758759-29629-2-git-send-email-Waiman.Long@hp.com> <1377751465.4028.20.camel@pasglop> <20130829070012.GC27322@gmail.com> <1377822408.4028.44.camel@pasglop> <20130830071612.GB14099@gmail.com> Date: Fri, 30 Aug 2013 08:28:33 -0700 X-Google-Sender-Auth: E682gSiyNEfpC_5e_LMgeK_GbG8 Message-ID: Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount From: Linus Torvalds To: Ingo Molnar Cc: Benjamin Herrenschmidt , Waiman Long , Alexander Viro , Jeff Layton , Miklos Szeredi , Ingo Molnar , Thomas Gleixner , linux-fsdevel , Linux Kernel Mailing List , Peter Zijlstra , Steven Rostedt , Andi Kleen , "Chandramouleeswaran, Aswin" , "Norton, Scott J" , Michael Neuling Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1515 Lines: 32 On Fri, Aug 30, 2013 at 12:16 AM, Ingo Molnar wrote: > > * Linus Torvalds wrote: > >> > BTW. Do you have your test case at hand ? >> >> My test-case is a joke. It's explicitly *trying* to get as much >> contention as possible on a dentry, by just starting up a lot of threads >> that look up one single pathname (the same one for everybody). It >> defaults to using /tmp for this, but you can specify the filename. > > Waiman's tests seemed to use sufficiently generic and varied workloads > (AIM7) and they showed pretty nice unconditional improvements with his > variant of this scheme, so I think testing with your simple testcase that > intentionally magnifies the scalability issue is 100% legit and may in > fact help tune the changes more accurately, because it has less inherent > noise. Yes. However, what I am (not very) worried about is that people will hit some particular codepath that ends up having bad behavior. I think I covered all the normal hotpaths in pathname lookup, which is why I'm not *that* worried, but it's still the case that my silly test-case is very limited. It's limited for a good *reason* (to try to show the worst-case scalability problem), but it's limited. Linus -- 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/