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 839D5C433F4 for ; Mon, 27 Aug 2018 10:25:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2AC70208D4 for ; Mon, 27 Aug 2018 10:25:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2AC70208D4 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 S1726947AbeH0OLu (ORCPT ); Mon, 27 Aug 2018 10:11:50 -0400 Received: from mga04.intel.com ([192.55.52.120]:17021 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726868AbeH0OLu (ORCPT ); Mon, 27 Aug 2018 10:11:50 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Aug 2018 03:25:47 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,294,1531810800"; d="scan'208";a="75890976" Received: from linux.intel.com ([10.54.29.200]) by FMSMGA003.fm.intel.com with ESMTP; 27 Aug 2018 03:25:38 -0700 Received: from [10.125.252.155] (abudanko-mobl.ccr.corp.intel.com [10.125.252.155]) by linux.intel.com (Postfix) with ESMTP id 6DAEE5803DA; Mon, 27 Aug 2018 03:25:36 -0700 (PDT) Subject: Re: [PATCH v2 2/2]: perf record: enable asynchronous trace writing To: Namhyung Kim Cc: Jiri Olsa , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Andi Kleen , linux-kernel , linux-perf-users@vger.kernel.org, kernel-team@lge.com References: <54cc11d7-3ef2-c856-052e-6e2c309ff743@linux.intel.com> <20180827083852.GF24695@krava> <20180827100536.GA8065@sejong> From: Alexey Budankov Organization: Intel Corp. Message-ID: <3c0a8ecc-a68e-7e19-066c-096f7e318e1f@linux.intel.com> Date: Mon, 27 Aug 2018 13:25:35 +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: <20180827100536.GA8065@sejong> 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 Namhyung, On 27.08.2018 13:05, Namhyung Kim wrote: > Hello, > > On Mon, Aug 27, 2018 at 12:33:07PM +0300, Alexey Budankov wrote: >> Hi, >> >> On 27.08.2018 11:38, Jiri Olsa wrote: >>> On Thu, Aug 23, 2018 at 07:47:01PM +0300, Alexey Budankov wrote: >>> >>> SNIP >>> >>>> static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist, >>>> bool overwrite) >>>> { >>>> u64 bytes_written = rec->bytes_written; >>>> - int i; >>>> - int rc = 0; >>>> + int i, rc = 0; >>>> struct perf_mmap *maps; >>>> + int trace_fd = rec->session->data->file.fd; >>>> + struct aiocb **mmap_aio = rec->evlist->mmap_aio; >>>> + int mmap_aio_size = 0; >>>> + off_t off; >>>> >>>> if (!evlist) >>>> return 0; >>>> @@ -546,14 +620,17 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli >>>> if (overwrite && evlist->bkw_mmap_state != BKW_MMAP_DATA_PENDING) >>>> return 0; >>>> >>>> + off = lseek(trace_fd, 0, SEEK_CUR); >>>> + >>> >>> with async write, do we need to query/set the offset like this >>> all the time? >> >> It looks like we need it this way. Internally glibc AIO implements writes >> using pwrite64 syscall in our case. The sycall requires offset as a parameter >> and doesn't update file position on the completion. >> >>> >>> could we just keep/update the offset value in the 'struct perf_data_file' >>> and skip both lseek calls? >> >> Don't see how it is possible. offset is different for every enqeued write >> operation and write areas don't intersect for the whole writing loop. >> To know the final file position it is required to iterate thru >> the loop. > > But as far as I can see the offset is linearly updated in > perf_mmap__push() and I guess those two lseek() calls will return > a same value as the last updated offset, no? Yes, offset is linearly calculated by perf_mmap__push() code for the next possible write operation, but file position is update by the kernel only in the second lseek() syscall after the loop. The first lseek() syscall reads that file position for the next loop iterations. Regards, Alexey > > Thanks, > Namhyung >