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 F0D7EC433F5 for ; Mon, 27 Aug 2018 10:49:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A3D67208B4 for ; Mon, 27 Aug 2018 10:49:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3D67208B4 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 S1727045AbeH0OfO (ORCPT ); Mon, 27 Aug 2018 10:35:14 -0400 Received: from mga05.intel.com ([192.55.52.43]:11274 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726883AbeH0OfO (ORCPT ); Mon, 27 Aug 2018 10:35:14 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Aug 2018 03:49:06 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,294,1531810800"; d="scan'208";a="78650178" Received: from linux.intel.com ([10.54.29.200]) by orsmga003.jf.intel.com with ESMTP; 27 Aug 2018 03:48:22 -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 61CFD5802B0; Mon, 27 Aug 2018 03:48:20 -0700 (PDT) Subject: Re: [PATCH v2 2/2]: perf record: enable asynchronous trace writing To: Jiri Olsa Cc: Namhyung Kim , 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> <3c0a8ecc-a68e-7e19-066c-096f7e318e1f@linux.intel.com> <20180827103819.GB3725@krava> From: Alexey Budankov Organization: Intel Corp. Message-ID: <2b595b40-fe31-2ced-6077-e972e4aaf561@linux.intel.com> Date: Mon, 27 Aug 2018 13:48:19 +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: <20180827103819.GB3725@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 On 27.08.2018 13:38, Jiri Olsa wrote: > On Mon, Aug 27, 2018 at 01:25:35PM +0300, Alexey Budankov wrote: >> 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; >>>>>> Hi >>>>>> + 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. > > does the file's offset need to get updated with lseek at all? > the async write gets offset.. so I'd think as long as we keep > offset value, we don't need to call lseek at all Yep, I expected the same from pwrite64() syscall which eventually gets this offset but that is not the case. > > jirka >