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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 657B0C433DF for ; Fri, 26 Jun 2020 19:39:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A581207D8 for ; Fri, 26 Jun 2020 19:39:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725836AbgFZTjO (ORCPT ); Fri, 26 Jun 2020 15:39:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:39122 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725780AbgFZTjO (ORCPT ); Fri, 26 Jun 2020 15:39:14 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EADC8206C0; Fri, 26 Jun 2020 19:39:11 +0000 (UTC) Date: Fri, 26 Jun 2020 15:39:10 -0400 From: Steven Rostedt To: Mathieu Desnoyers Cc: linux-kernel , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Masami Hiramatsu , Arnaldo Carvalho de Melo , Jiri Olsa , Namhyung Kim , Yordan Karadzhov , Tzvetomir Stoyanov , Tom Zanussi , Jason Behmer , Julia Lawall , Clark Williams , bristot , Daniel Wagner , Darren Hart , Jonathan Corbet , "Suresh E. Warrier" Subject: Re: [RFC][PATCH] ring-buffer: Have nested events still record running time stamp Message-ID: <20200626153910.7b3d7e16@oasis.local.home> In-Reply-To: <20200626145819.0d3cae3c@oasis.local.home> References: <20200625094454.732790f7@oasis.local.home> <1548518134.13177.1593107707149.JavaMail.zimbra@efficios.com> <20200625143525.2f3a2902@oasis.local.home> <79426976.13417.1593113702719.JavaMail.zimbra@efficios.com> <20200625223611.1dbb3b35@oasis.local.home> <20200625233552.2c8a0d1e@oasis.local.home> <20200626095801.14cfa8a3@oasis.local.home> <304619857.14491.1593195230002.JavaMail.zimbra@efficios.com> <20200626145819.0d3cae3c@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 26 Jun 2020 14:58:19 -0400 Steven Rostedt wrote: > Second usage: > > /* SLOW PATH - Interrupted between A and C */ > a_ok = rb_time_read(&cpu_buffer->write_stamp, &after); > ts = rb_time_stamp(cpu_buffer->buffer); > barrier(); > /*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) && > a_ok && after < ts) { > /* Nothing came after this event between C and E */ > info->delta = ts - after; > (void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, info->ts); > info->ts = ts; > } else { > info->delta = 0; Actually, I don't think a_ok can every be false here. An uninterrupted event will leave with both before_stamp and write_stamp valid. As an uninterrupted event will write to both (and a rb_time_t is only invalid from reading an interrupted event). To get to this path we have: w = local_read(write_tail); <--- Interrupt event (makes write_stamp valid!) write = local_add_return(write_tail, length); w != write - length; [..] a_ok = rb_time_read(write_stamp); Must always be valid! -- Steve