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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 A053CC65C20 for ; Mon, 8 Oct 2018 15:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7132220652 for ; Mon, 8 Oct 2018 15:39:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7132220652 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727051AbeJHWvp (ORCPT ); Mon, 8 Oct 2018 18:51:45 -0400 Received: from mga07.intel.com ([134.134.136.100]:35133 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726391AbeJHWvp (ORCPT ); Mon, 8 Oct 2018 18:51:45 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 08 Oct 2018 08:39:26 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,357,1534834800"; d="scan'208";a="76345616" Received: from linux.intel.com ([10.54.29.200]) by fmsmga007.fm.intel.com with ESMTP; 08 Oct 2018 08:39:26 -0700 Received: from [10.252.30.144] (abudanko-mobl.ccr.corp.intel.com [10.252.30.144]) by linux.intel.com (Postfix) with ESMTP id B9D8F580145; Mon, 8 Oct 2018 08:39:23 -0700 (PDT) Subject: Re: [PATCH v11 2/3]: perf record: enable asynchronous trace writing To: Jiri Olsa Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Namhyung Kim , Andi Kleen , linux-kernel References: <7d42aa80-8e69-44e4-b963-e8ef89df2099@linux.intel.com> <31b0ae5f-e1b5-4255-11af-46c8ebe8e2be@linux.intel.com> <20181008105254.GG17270@krava> <20181008125310.GF18757@krava> <20181008151108.GH18757@krava> From: Alexey Budankov Organization: Intel Corp. Message-ID: <1548bd97-4d8f-f0b6-3a37-b3f2e464ff7d@linux.intel.com> Date: Mon, 8 Oct 2018 18:39:21 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181008151108.GH18757@krava> 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 Hi, On 08.10.2018 18:11, Jiri Olsa wrote: > On Mon, Oct 08, 2018 at 05:42:18PM +0300, Alexey Budankov wrote: >> Hi, >> On 08.10.2018 15:53, Jiri Olsa wrote: >>> On Mon, Oct 08, 2018 at 03:24:31PM +0300, Alexey Budankov wrote: >>>> Hi, >>>> >>>> On 08.10.2018 13:52, Jiri Olsa wrote: >>>>> On Mon, Oct 08, 2018 at 09:17:11AM +0300, Alexey Budankov wrote: >>>> >>>>>> +#ifdef HAVE_AIO_SUPPORT >>>>>> + off = lseek(trace_fd, 0, SEEK_CUR); >>>>>> +#endif >>>>> >>>>> I'm still little puzzled why we need to do this, >>>>> when the aio write takes the offset value, but >>>> >>>> pwrite() syscall [1] which is the base for aio_write() doesn't >>>> advance file pos value so it requires to be calculated and >>>> updated by callers of aio_write() API. >>> >>> ok, so aio_write does not need the offset to be updated, >>> who needs it then? >> >> aio_write() needs this offset as an input parameter. >> aio_write() gets offset as a part of cblock object. > > yes, it's an 'arg' to aio_write syscall > >> Adjacent aio_write() records should not overlap in the trace file so >> off value is incremented by size in every loop iteration after >> successful aio_write() call. > > but does the aio_write need the lseek 'set' call? if not, we could Yes, lseek(,, SEEK_SET) is still required after the loop, so the next synchronous records would go after AIO written parts that might be still *in-flight* by that time. Thanks, Alexey > keep the 'offset' value within perf (like in the struct perf_data_file > or struct record) without any need to call lseek > > jirka >