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 568B8C433EF for ; Wed, 9 Feb 2022 18:20:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239298AbiBISUO (ORCPT ); Wed, 9 Feb 2022 13:20:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239128AbiBIST4 (ORCPT ); Wed, 9 Feb 2022 13:19:56 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 34AC4C03C1AA for ; Wed, 9 Feb 2022 10:19:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1644430761; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Qax2p4QYoRES22yBVTV0pqT1gnZb7y7VCXsID9Egc7E=; b=L0mrJIQD61P+grJo6m1ZDIH5iYbwFQGbAmk/dDNFrOdm9xO+y/6nt9QIiEIBSYQSpAjwSy klzIaxGN2GC1Dfw/pDxbehdDOtxnRgqKT9g3JzF3PW4/MmXg3e4igfs7W6xtuWqE546fQ/ 7/kJIwm4+uUSGBYMscX6ovY/537caXk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-620-zHSc6UrVO8a503hE2f2VtA-1; Wed, 09 Feb 2022 13:19:15 -0500 X-MC-Unique: zHSc6UrVO8a503hE2f2VtA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 68A4881433D; Wed, 9 Feb 2022 18:19:11 +0000 (UTC) Received: from [10.22.9.207] (unknown [10.22.9.207]) by smtp.corp.redhat.com (Postfix) with ESMTP id 887577DE57; Wed, 9 Feb 2022 18:19:08 +0000 (UTC) Message-ID: <24fe6a08-5931-8e8d-8d77-459388c4654e@redhat.com> Date: Wed, 9 Feb 2022 13:19:07 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [RFC 00/12] locking: Separate lock tracepoints from lockdep/lock_stat (v1) Content-Language: en-US To: Peter Zijlstra , Namhyung Kim Cc: Ingo Molnar , Will Deacon , Boqun Feng , LKML , Thomas Gleixner , Steven Rostedt , Byungchul Park , "Paul E. McKenney" , Mathieu Desnoyers , Radoslaw Burny , Tejun Heo , rcu@vger.kernel.org, cgroups@vger.kernel.org, linux-btrfs@vger.kernel.org, intel-gfx@lists.freedesktop.org References: <20220208184208.79303-1-namhyung@kernel.org> <20220209090908.GK23216@worktop.programming.kicks-ass.net> From: Waiman Long In-Reply-To: <20220209090908.GK23216@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/9/22 04:09, 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. > > Yes, the name is convenient, but it's just not worth it IMO. It makes > the whole proposition too much of a trade-off. > > Would it not be possible to reconstruct enough useful information from > the lock callsite? > I second that as I don't want to see the size of a spinlock exceeds 4 bytes in a production system. Instead of storing additional information (e.g. lock name) directly into the lock itself. Maybe we can store it elsewhere and use the lock address as the key to locate it in a hash table. We can certainly extend the various lock init functions to do that. It will be trickier for statically initialized locks, but we can probably find a way to do that too. Cheers, Longman