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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 DD2ECC65C20 for ; Mon, 8 Oct 2018 15:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A06682075C for ; Mon, 8 Oct 2018 15:11:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A06682075C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.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 S1726569AbeJHWXW (ORCPT ); Mon, 8 Oct 2018 18:23:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32424 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726078AbeJHWXW (ORCPT ); Mon, 8 Oct 2018 18:23:22 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 63785811AC; Mon, 8 Oct 2018 15:11:11 +0000 (UTC) Received: from krava (unknown [10.43.17.152]) by smtp.corp.redhat.com (Postfix) with SMTP id AA4C25C554; Mon, 8 Oct 2018 15:11:09 +0000 (UTC) Date: Mon, 8 Oct 2018 17:11:08 +0200 From: Jiri Olsa To: Alexey Budankov Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Namhyung Kim , Andi Kleen , linux-kernel Subject: Re: [PATCH v11 2/3]: perf record: enable asynchronous trace writing Message-ID: <20181008151108.GH18757@krava> References: <7d42aa80-8e69-44e4-b963-e8ef89df2099@linux.intel.com> <31b0ae5f-e1b5-4255-11af-46c8ebe8e2be@linux.intel.com> <20181008105254.GG17270@krava> <20181008125310.GF18757@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 08 Oct 2018 15:11:11 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 keep the 'offset' value within perf (like in the struct perf_data_file or struct record) without any need to call lseek jirka