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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B3222C433F5 for ; Wed, 9 Feb 2022 19:02:49 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 507D510E57C; Wed, 9 Feb 2022 19:02:49 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id AF47B10E58D for ; Wed, 9 Feb 2022 19:02:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1644433366; 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=UuA86Nyzl5Eui91dzFfwf9ECfs1Xn0BsmmUF+q9vMTM=; b=WFN1jVe4x10xJLhthQGCKyFtrPclzt6dPAkBTBStn5zy2Mm9m3tnwAWPvi9UHVf+zvSSbx FhwUtfTKhhH0M6oQ+GQN7Kx38t6gdhcpgAlJVT917X+wevUtv6xUFhB3wLbrUuvpjM4T5/ 2PksfqStlLVlnneUJjuFcYVUWsfjnwE= 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-258-3vO76ThsNKa4dxfImmOr4g-1; Wed, 09 Feb 2022 14:02:40 -0500 X-MC-Unique: 3vO76ThsNKa4dxfImmOr4g-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B83311966323; Wed, 9 Feb 2022 19:02:37 +0000 (UTC) Received: from [10.22.9.207] (unknown [10.22.9.207]) by smtp.corp.redhat.com (Postfix) with ESMTP id 69C2410013C1; Wed, 9 Feb 2022 19:02:35 +0000 (UTC) Message-ID: <69e5f778-8715-4acf-c027-58b6ec4a9e77@redhat.com> Date: Wed, 9 Feb 2022 14:02:34 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Content-Language: en-US To: Mathieu Desnoyers References: <20220208184208.79303-1-namhyung@kernel.org> <20220209090908.GK23216@worktop.programming.kicks-ass.net> <24fe6a08-5931-8e8d-8d77-459388c4654e@redhat.com> <919214156.50301.1644431371345.JavaMail.zimbra@efficios.com> From: Waiman Long In-Reply-To: <919214156.50301.1644431371345.JavaMail.zimbra@efficios.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Subject: Re: [Intel-gfx] [RFC 00/12] locking: Separate lock tracepoints from lockdep/lock_stat (v1) X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rcu , intel-gfx@lists.freedesktop.org, Peter Zijlstra , Boqun Feng , linux-kernel , rostedt , Radoslaw Burny , Byungchul Park , "Paul E. McKenney" , cgroups , Tejun Heo , Namhyung Kim , Thomas Gleixner , Will Deacon , Ingo Molnar , linux-btrfs Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 2/9/22 13:29, Mathieu Desnoyers wrote: > ----- On Feb 9, 2022, at 1:19 PM, Waiman Long longman@redhat.com wrote: > >> 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. > If we go down that route, it would be nice if we can support a few different > use-cases for various tracers out there. > > One use-case (a) requires the ability to query the lock name based on its address as key. > For this a hash table is a good fit. This would allow tracers like ftrace to > output lock names in its human-readable output which is formatted within the kernel. > > Another use-case (b) is to be able to "dump" the lock { name, address } tuples > into the trace stream (we call this statedump events in lttng), and do the > translation from address to name at post-processing. This simply requires > that this information is available for iteration for both the core kernel > and module locks, so the tracer can dump this information on trace start > and module load. > > Use-case (b) is very similar to what is done for the kernel tracepoints. Based > on this, implementing the init code that iterates on those sections and populates > a hash table for use-case (a) should be easy enough. Yes, that are good use cases for this type of functionality. I do need to think about how to do it for statically initialized lock first. Thanks, Longman