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 9ABDDC761AF for ; Wed, 5 Apr 2023 16:26:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233118AbjDEQ0K (ORCPT ); Wed, 5 Apr 2023 12:26:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229479AbjDEQ0I (ORCPT ); Wed, 5 Apr 2023 12:26:08 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47D9ACA; Wed, 5 Apr 2023 09:26:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1680711965; x=1712247965; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=OBPArDpGTZjCLqy9R4ICyoG2JGVamWpModrhzwKQTJE=; b=eQEZrZKM4DS0aZKPJ5TE/Hch5M/Q8kA/g5vhMnfUej1ou9egQueYeSgd tSM4Vei2GeyuyFyF8AXNwIaou4pisOg2kCQx3Auh+gQVJC6hbzSE8ygqk rQ08vjOz9mS3A5tx3DH7ZC6ClSvzsKWTO7DBHDH9SVzXbZ7Ldf+GXeZVt cQsfkUcXXCFRnUKtqolcQe/QOp1ED2sG+/vfH3rQrweHDzWo46zXIHlQY YkZOsaIWO0iAG4jgcq4rUy/LmxEHvobwUffv6lsoh9bXchEMc4H+x/Ov0 S++BfuEdkOfZD5F3E2Utxhb+yCVuaEBhqLLTVvAYX8XYxLvDHY8Gg8MGI A==; X-IronPort-AV: E=McAfee;i="6600,9927,10671"; a="428787799" X-IronPort-AV: E=Sophos;i="5.98,321,1673942400"; d="scan'208";a="428787799" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Apr 2023 09:25:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10671"; a="686806956" X-IronPort-AV: E=Sophos;i="5.98,321,1673942400"; d="scan'208";a="686806956" Received: from ahunter6-mobl1.ger.corp.intel.com (HELO [10.0.2.15]) ([10.252.42.88]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Apr 2023 09:25:32 -0700 Message-ID: <2aaba740-35e4-4a68-2676-63d47898378c@intel.com> Date: Wed, 5 Apr 2023 19:25:27 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.9.1 Subject: Re: [PATCH v5 00/17] Reference count checker and related fixes Content-Language: en-US To: Arnaldo Carvalho de Melo Cc: Ian Rogers , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Darren Hart , Davidlohr Bueso , James Clark , John Garry , Riccardo Mancini , Yury Norov , Andy Shevchenko , Andrew Morton , Leo Yan , Andi Kleen , Thomas Richter , Kan Liang , Madhavan Srinivasan , Shunsuke Nakamura , Song Liu , Masami Hiramatsu , Steven Rostedt , Miaoqian Lin , Stephen Brennan , Kajol Jain , Alexey Bayduraev , German Gomez , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Dumazet , Dmitry Vyukov , Hao Luo , Stephane Eranian References: <20230320212248.1175731-1-irogers@google.com> <7443d427-783b-44b6-85e6-5e667bb83a94@intel.com> <527b8bcb-d462-5fff-5310-703b55902a61@intel.com> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/04/23 16:20, Arnaldo Carvalho de Melo wrote: > Em Wed, Apr 05, 2023 at 11:47:26AM +0300, Adrian Hunter escreveu: >> On 4/04/23 21:54, Arnaldo Carvalho de Melo wrote: >>> Em Tue, Apr 04, 2023 at 03:41:38PM -0300, Arnaldo Carvalho de Melo escreveu: >>>> Em Tue, Apr 04, 2023 at 08:25:41PM +0300, Adrian Hunter escreveu: >>>>> On 4/04/23 18:58, Ian Rogers wrote: >>>>>> Ping. It would be nice to have this landed or at least the first 10 >>>>>> patches that refactor the map API and are the bulk of the >>>>>> lines-of-code changed. Having those landed would make it easier to >>>>>> rebase in the future, but I also think the whole series is ready to >>>>>> go. >>>>> >>>>> I was wondering if the handling of dynamic data like struct map makes >>>>> any sense at present. Perhaps someone can reassure me. >>>>> >>>>> A struct map can be updated when an MMAP event is processed. So it >>>> >>>> Yes, it can, and the update is made via a new PERF_RECORD_MMAP, right? >>>> >>>> So: >>>> >>>> perf_event__process_mmap() >>>> machine__process_mmap2_event() >>>> map__new() + thread__insert_map(thread, map) >>>> maps__fixup_overlappings() >>>> maps__insert(thread->maps, map); >>>> >>>> Ok, from this point on new samples on ] map->start .. map->end ] will >>>> grab a refcount to this new map in its hist_entry, right? >>>> >>>> When we want to sort by dso we will look at hist_entry->map->dso, etc. >>> >>> And in 'perf top' we go decaying hist entries, when we delete the >>> hist_entry, drop the reference count to things it holds, that will then >>> be finally deleted when no more hist_entries point to it. >>> >>>>> seems like anything racing with event processing is already broken, and >>>>> reference counting / locking cannot help - unless there is also >>>>> copy-on-write (which there isn't at present)? > >> So I checked, and struct map *is* copy-on-write in >> maps__fixup_overlappings(), so that should not be a problem. > >>>>> For struct maps, referencing it while simultaneously processing >>>>> events seems to make even less sense? > >>>> Can you elaborate some more? > >> Only that the maps are not necessarily stable e.g. the map that you >> need has been replaced in the meantime. > > Well, it may be sliced in several or shrunk by new ones overlapping it, > but it if completely disappears, say a new map starts before the one > disappearing and ends after it, then it remains with reference counts if > there are hist_entries (or other data structure) pointing to them, > right? > >> But upon investigation, the only user at the moment is >> maps__find_ams(). If we kept the removed maps (we used to), >> it might be possible to make maps__find_ams() work correctly >> in any case. > > Humm, I think I see what you mean, maps__find_ams() is called when we > are annotating a symbol, not when we're processing a sample, so it may > be the case that at the time of annotation the executable that is being > found (its parsing the target IP of a 'call' assembly instruction) was > replaced, is that the case? Yes, that is the possibility