From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD71AC4332F for ; Thu, 10 Feb 2022 20:11:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344129AbiBJULC (ORCPT ); Thu, 10 Feb 2022 15:11:02 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:32882 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238091AbiBJULB (ORCPT ); Thu, 10 Feb 2022 15:11:01 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 93DE42735; Thu, 10 Feb 2022 12:11:01 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 3F912B8272A; Thu, 10 Feb 2022 20:11:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAAD1C004E1; Thu, 10 Feb 2022 20:10:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644523858; bh=iLVxmxOrhgeAZwTkFuG1YJotZgqgklwTkad+usc+SbM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=o56gSkY6KjsTqaNLucwpbwSfiS6lwFJGp+betDu9X8aq4l5khh7ZxFWlsuOatT/SU kOGdUu/H0ffGyVffjwXC/ybeD43ppXkNTvDupxItbHL7c25YO9JTjYo5liSOPlcZC2 S1l9sx6T5hVnihTP/6rf8lhrpqqKkZFEIUwl5KM59cYjlYCu/0Yr+pjZ3xGxIECloB CApZ1rDMi8muJMOR27g2MNZAWOGq2UPWWAP3ejtxogM0Zp3M0cGAvHvgqTg5t4J52t BAlD+tYaAE1gb9pplHq+kCcw19EB/b00N+HnvtaBqE+Exhnq3oBWfkbhFmD3qaQRE5 TDTWUZVxVnWFA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 9B70E5C0439; Thu, 10 Feb 2022 12:10:58 -0800 (PST) Date: Thu, 10 Feb 2022 12:10:58 -0800 From: "Paul E. McKenney" To: Waiman Long Cc: Peter Zijlstra , Namhyung Kim , Ingo Molnar , Will Deacon , Boqun Feng , LKML , Thomas Gleixner , Steven Rostedt , Byungchul Park , Mathieu Desnoyers , Radoslaw Burny , Tejun Heo , rcu , cgroups , linux-btrfs , intel-gfx Subject: Re: [RFC 00/12] locking: Separate lock tracepoints from lockdep/lock_stat (v1) Message-ID: <20220210201058.GP4285@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220208184208.79303-1-namhyung@kernel.org> <20220209090908.GK23216@worktop.programming.kicks-ass.net> <20220210191404.GM4285@paulmck-ThinkPad-P17-Gen-1> <52de2e14-33d9-bdda-4b37-3e72ae9954c7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52de2e14-33d9-bdda-4b37-3e72ae9954c7@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 10, 2022 at 02:27:11PM -0500, Waiman Long wrote: > On 2/10/22 14:14, Paul E. McKenney wrote: > > On Thu, Feb 10, 2022 at 10:13:53AM +0100, Peter Zijlstra wrote: > > > On Wed, Feb 09, 2022 at 04:32:58PM -0800, Namhyung Kim wrote: > > > > On Wed, Feb 9, 2022 at 1:09 AM Peter Zijlstra wrote: > > > > > On Tue, Feb 08, 2022 at 10:41:56AM -0800, Namhyung Kim wrote: > > > > > > > > > > > Eventually I'm mostly interested in the contended locks only and I > > > > > > want to reduce the overhead in the fast path. By moving that, it'd be > > > > > > easy to track contended locks with timing by using two tracepoints. > > > > > So why not put in two new tracepoints and call it a day? > > > > > > > > > > Why muck about with all that lockdep stuff just to preserve the name > > > > > (and in the process continue to blow up data structures etc..). This > > > > > leaves distros in a bind, will they enable this config and provide > > > > > tracepoints while bloating the data structures and destroying things > > > > > like lockref (which relies on sizeof(spinlock_t)), or not provide this > > > > > at all. > > > > If it's only lockref, is it possible to change it to use arch_spinlock_t > > > > so that it can remain in 4 bytes? It'd be really nice if we can keep > > > > spin lock size, but it'd be easier to carry the name with it for > > > > analysis IMHO. > > > It's just vile and disgusting to blow up the lock size for convenience > > > like this. > > > > > > And no, there's more of that around. A lot of effort has been spend to > > > make sure spinlocks are 32bit and we're not going to give that up for > > > something as daft as this. > > > > > > Just think harder on the analysis side. Like said; I'm thinking the > > > caller IP should be good enough most of the time. > > > > Another option is to keep any additional storage in a separate data > > structure keyed off of lock address, lockdep class, or whatever. > > > > Whether or not this is a -good- option, well, who knows? ;-) > > I have suggested that too. Unfortunately, I was replying to an email with > your wrong email address. So you might not have received it. Plus I was too lazy to go look at lore. ;-) For whatever it is worth, we did something similar in DYNIX/ptx, whose spinlocks were limited to a single byte. But it does have its drawbacks. Thanx, Paul