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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8CDEEC433E0 for ; Wed, 20 May 2020 05:36:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 690EB2075F for ; Wed, 20 May 2020 05:36:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726634AbgETFgo (ORCPT ); Wed, 20 May 2020 01:36:44 -0400 Received: from mga17.intel.com ([192.55.52.151]:58244 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726309AbgETFgo (ORCPT ); Wed, 20 May 2020 01:36:44 -0400 IronPort-SDR: 6QE4SB5lb+7MX0ZJbG35mFZ9Zh9eGY46aS790F4EYM8LiAQOrsDlBNhrqQmkPdKbwer1EvBMkO XEEfDTRpzrdw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 May 2020 22:36:43 -0700 IronPort-SDR: 87gc2lov21YAmGt3hHVbONHx3bH/K5qKm/iMkLTJkaMCftMIYpxn4KPqrUtVoJ19OBanL+diPi Yn+sAvLNj6bA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,412,1583222400"; d="scan'208";a="373965863" Received: from yjin15-mobl1.ccr.corp.intel.com (HELO [10.238.5.239]) ([10.238.5.239]) by fmsmga001.fm.intel.com with ESMTP; 19 May 2020 22:36:41 -0700 Subject: Re: [PATCH] perf evsel: Get group fd from CPU0 for system wide event From: "Jin, Yao" To: Jiri Olsa Cc: acme@kernel.org, jolsa@kernel.org, peterz@infradead.org, mingo@redhat.com, alexander.shishkin@linux.intel.com, Linux-kernel@vger.kernel.org, ak@linux.intel.com, kan.liang@intel.com, yao.jin@intel.com References: <20200430013451.17196-1-yao.jin@linux.intel.com> <20200501102337.GA1761222@krava> <20200505000352.GH1916255@krava> <3e813227-4954-0d4b-bc7a-ca272b18454a@linux.intel.com> <68e53765-6f45-9483-7543-0a2f961cdc62@linux.intel.com> <20200515083312.GB3511648@krava> <5fe2efe4-f8a3-04ef-f5e8-7b9c433d4142@linux.intel.com> Message-ID: <82da23c8-94dd-4096-a987-a17087e2642f@linux.intel.com> Date: Wed, 20 May 2020 13:36:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <5fe2efe4-f8a3-04ef-f5e8-7b9c433d4142@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jiri, On 5/18/2020 11:28 AM, Jin, Yao wrote: > Hi Jiri, > > On 5/15/2020 4:33 PM, Jiri Olsa wrote: >> On Fri, May 15, 2020 at 02:04:57PM +0800, Jin, Yao wrote: >> >> SNIP >> >>> I think I get the root cause. That should be a serious bug in get_group_fd, access violation! >>> >>> For a group mixed with system-wide event and per-core event and the group >>> leader is system-wide event, access violation will happen. >>> >>> perf_evsel__alloc_fd allocates one FD member for system-wide event (only FD(evsel, 0, 0) is valid). >>> >>> But for per core event, perf_evsel__alloc_fd allocates N FD members (N = >>> ncpus). For example, for ncpus is 8, FD(evsel, 0, 0) to FD(evsel, 7, 0) are >>> valid. >>> >>> get_group_fd(struct evsel *evsel, int cpu, int thread) >>> { >>>      struct evsel *leader = evsel->leader; >>> >>>      fd = FD(leader, cpu, thread);    /* access violation may happen here */ >>> } >>> >>> If leader is system-wide event, only the FD(leader, 0, 0) is valid. >>> >>> When get_group_fd accesses FD(leader, 1, 0), access violation happens. >>> >>> My fix is: >>> >>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c >>> index 28683b0eb738..db05b8a1e1a8 100644 >>> --- a/tools/perf/util/evsel.c >>> +++ b/tools/perf/util/evsel.c >>> @@ -1440,6 +1440,9 @@ static int get_group_fd(struct evsel *evsel, int cpu, int thread) >>>          if (evsel__is_group_leader(evsel)) >>>                  return -1; >>> >>> +       if (leader->core.system_wide && !evsel->core.system_wide) >>> +               return -2; >> >> so this effectively stops grouping system_wide events with others, >> and I think it's correct, how about events that differ in cpumask? >> > > My understanding for the events that differ in cpumaks is, if the leader's cpumask is not fully > matched with the evsel's cpumask then we stop the grouping. Is this understanding correct? > > I have done some tests and get some conclusions: > > 1. If the group is mixed with core and uncore events, the system_wide checking can distinguish them. > > 2. If the group is mixed with core and uncore events and "-a" is specified, the system_wide for core > event is also false. So system_wide checking can distinguish them too > > 3. In my test, the issue only occurs when we collect the metric which is mixed with uncore event and > core event, so maybe checking the system_wide is OK. > >> should we perhaps ensure this before we call open? go throught all >> groups and check they are on the same cpus? >> > > The issue doesn't happen at most of the time (only for the metric consisting of uncore event and > core event), so fallback to stop grouping if call open is failed looks reasonable. > > Thanks > Jin Yao > >> thanks, >> jirka >> >> >>> + >>>          /* >>>           * Leader must be already processed/open, >>>           * if not it's a bug. >>> @@ -1665,6 +1668,11 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus, >>>                                  pid = perf_thread_map__pid(threads, thread); >>> >>>                          group_fd = get_group_fd(evsel, cpu, thread); >>> +                       if (group_fd == -2) { >>> +                               errno = EINVAL; >>> +                               err = -EINVAL; >>> +                               goto out_close; >>> +                       } >>>   retry_open: >>>                          test_attr__ready(); >>> >>> It enables the perf_evlist__reset_weak_group. And in the second_pass (in >>> __run_perf_stat), the events will be opened successfully. >>> >>> I have tested OK for this fix on cascadelakex. >>> >>> Thanks >>> Jin Yao >>> >> Is this fix OK? Another thing is, do you think if we need to rename "evsel->core.system_wide" to "evsel->core.has_cpumask". The "system_wide" may misleading. evsel->core.system_wide = pmu ? pmu->is_uncore : false; "pmu->is_uncore" is true if PMU has a "cpumask". But it's not just uncore PMU which has cpumask. Some other PMUs, e.g. cstate_pkg, also have cpumask. So for this case, "has_cpumask" should be better. But I'm not sure if the change is OK for other case, e.g. PT, which also uses "evsel->core.system_wide". Thanks Jin Yao