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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 49850C433DF for ; Mon, 29 Jun 2020 18:57:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3587E20663 for ; Mon, 29 Jun 2020 18:57:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730110AbgF2S5g (ORCPT ); Mon, 29 Jun 2020 14:57:36 -0400 Received: from mga05.intel.com ([192.55.52.43]:57279 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729847AbgF2S5d (ORCPT ); Mon, 29 Jun 2020 14:57:33 -0400 IronPort-SDR: 6vsMOgbGYcMt1ZHGcMZSH+75h2h0ld/P6ibxsCj3/Gnyp8RzoS9kxsqZvLp3+QG7O4O9Dq2fJH PN/yM3eh5T/A== X-IronPort-AV: E=McAfee;i="6000,8403,9666"; a="230816141" X-IronPort-AV: E=Sophos;i="5.75,295,1589266800"; d="scan'208";a="230816141" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2020 08:12:12 -0700 IronPort-SDR: j2KamSBj8xliJFX76goLSWvtUaCr1ceFqJcdJUpb5K/K1mEEwtccZaF4zdMF9IvsBvgRkEjMiw uzCCpDkS/bhg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,295,1589266800"; d="scan'208";a="318198466" Received: from linux.intel.com ([10.54.29.200]) by orsmga007.jf.intel.com with ESMTP; 29 Jun 2020 08:11:58 -0700 Received: from [10.249.227.168] (abudanko-mobl.ccr.corp.intel.com [10.249.227.168]) by linux.intel.com (Postfix) with ESMTP id 491A9580107; Mon, 29 Jun 2020 08:11:53 -0700 (PDT) From: Alexey Budankov Subject: Re: [PATCH v8 01/13] tools/libperf: avoid moving of fds at fdarray__filter() call To: Jiri Olsa , Arnaldo Carvalho de Melo Cc: Namhyung Kim , Alexander Shishkin , Peter Zijlstra , Ingo Molnar , Andi Kleen , linux-kernel References: <0781a077-aa82-5b4a-273e-c17372a72b93@linux.intel.com> <3d36dc7a-4249-096c-7554-80e6d290eac5@linux.intel.com> <20200625171405.GL2719003@krava> <688910f3-289e-d63e-79e3-0a17a6df0e9e@linux.intel.com> <20200626093745.GM2719003@krava> <6582201a-9570-709f-f6e9-5a644296f49d@linux.intel.com> Organization: Intel Corp. Message-ID: Date: Mon, 29 Jun 2020 18:11:52 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <6582201a-9570-709f-f6e9-5a644296f49d@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26.06.2020 13:06, Alexey Budankov wrote: > > On 26.06.2020 12:37, Jiri Olsa wrote: >> On Thu, Jun 25, 2020 at 10:32:29PM +0300, Alexey Budankov wrote: >>> >>> On 25.06.2020 20:14, Jiri Olsa wrote: >>>> On Wed, Jun 24, 2020 at 08:19:32PM +0300, Alexey Budankov wrote: >>>>> >>>>> On 17.06.2020 11:35, Alexey Budankov wrote: >>>>>> >>>>>> Skip fds with zeroed revents field from count and avoid fds moving >>>>>> at fdarray__filter() call so fds indices returned by fdarray__add() >>>>>> call stay the same and can be used for direct access and processing >>>>>> of fd revents status field at entries array of struct fdarray object. >>>>>> >>>>>> Signed-off-by: Alexey Budankov >>>>>> --- >>>>>> tools/lib/api/fd/array.c | 11 +++++------ >>>>>> tools/perf/tests/fdarray.c | 20 ++------------------ >>>>>> 2 files changed, 7 insertions(+), 24 deletions(-) >>>>>> >>>>>> diff --git a/tools/lib/api/fd/array.c b/tools/lib/api/fd/array.c >>>>>> index 58d44d5eee31..97843a837370 100644 >>>>>> --- a/tools/lib/api/fd/array.c >>>>>> +++ b/tools/lib/api/fd/array.c >>>>>> @@ -93,22 +93,21 @@ int fdarray__filter(struct fdarray *fda, short revents, >>>>>> return 0; >>>>>> >>>>>> for (fd = 0; fd < fda->nr; ++fd) { >>>>>> + if (!fda->entries[fd].revents) >>>>>> + continue; >>>>>> + >>>>> >>>>> So it looks like this condition also filters out non signaling events fds, not only >>>>> control and others fds, and this should be somehow avoided so such event related fds >>>>> would be counted. Several options have been proposed so far: >>>>> >>>>> 1) Explicit typing of fds via API extension and filtering based on the types: >>>>> a) with separate fdarray__add_stat() call >>>>> b) with type arg of existing fdarray__add() call >>>>> c) various memory management design is possible >>>>> >>>>> 2) Playing tricks with fd positions inside entries and assumptions on fdarray API calls ordering >>>>> - looks more like a hack than a designed solution >>>>> >>>>> 3) Rewrite of fdarray class to allocate separate object for every added fds >>>>> - can be replaced with nonscrewing of fds by __filter() >>>>> >>>>> 4) Distinct between fds types at fdarray__filter() using .revents == 0 condition >>>>> - seems to have corner cases and thus not applicable >>>>> >>>>> 5) Extension of fdarray__poll(, *arg_ptr, arg_size) with arg of fds array to atomically poll >>>>> on fdarray_add()-ed fds and external arg fds and then external arg fds processing >>>>> >>>>> 6) Rewrite of fdarray class on epoll() call basis >>>>> - introduces new scalability restrictions for Perf tool >>>> >>>> hum, how many fds for polling do you expect in your workloads? >>> >>> Currently it is several hundreds so default of 1K is easily hit and >>> "Profile a Large Number of PMU Events on Multi-Core Systems" section [1] >>> recommends: >>> >>> soft nofile 65535 >>> hard nofile 65535 >> >> I'm confused, are you talking about file descriptors limit now? >> this wont be affected by epoll change.. what do I miss? > > Currently there is already uname -n limit on the amount of open file descriptors > and Perf tool process is affected by that limit. > > Moving to epoll() will impose one more max_user_watches limit and that can additionally > confine Perf applicability even though default value on some machines currently > is high enough. Prior making v9 I would prefer to agree on some design to be implemented in order to avoid guessing and redundant reiterating. Options that I see as good balanced ones are 1) or 5), + non screwing of fds to fix staleness of pos(=fdarray__add()). Are there any thoughts so far? ~Aleksei