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,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 2EA39C433E0 for ; Fri, 26 Jun 2020 03:35:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 03BC720775 for ; Fri, 26 Jun 2020 03:35:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728397AbgFZDf4 (ORCPT ); Thu, 25 Jun 2020 23:35:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:49818 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725830AbgFZDf4 (ORCPT ); Thu, 25 Jun 2020 23:35:56 -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 05A3E20709; Fri, 26 Jun 2020 03:35:53 +0000 (UTC) Date: Thu, 25 Jun 2020 23:35:52 -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: <20200625233552.2c8a0d1e@oasis.local.home> In-Reply-To: <20200625223611.1dbb3b35@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> 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 Thu, 25 Jun 2020 22:36:11 -0400 Steven Rostedt wrote: > +static void rb_time_set(rb_time_t *t, u64 val) > +{ > + struct rb_time_read r; > + > + rb_time_read_set(&r, val); > + > + do { > + r.start_cnt = local_inc_return(&t->start_cnt); > + local_set(&t->top, r.top); > + local_set(&t->bottom, r.bottom); > + local_set(&t->end_cnt, r.start_cnt); > + } while (r.start_cnt != local_read(&t->start_cnt)); > +} > + > +static bool rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set) > +{ > + unsigned long ret; > + > + ret = local_cmpxchg(l, expect, set); > + return ret == expect; > +} > + > +static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set) > +{ > + struct rb_time_read e, s; > + > + rb_time_read_set(&e, expect); > + rb_time_read_set(&s, set); > + > + e.start_cnt = local_read(&t->start_cnt); > + e.end_cnt = local_read(&t->end_cnt); > + > + s.start_cnt = e.start_cnt + 1; > + s.end_cnt = e.start_cnt; > + > + if (!rb_time_read_cmpxchg(&t->start_cnt, e.start_cnt, s.start_cnt)) > + return false; > + if (!rb_time_read_cmpxchg(&t->top, e.top, s.top)) > + return false; > + if (!rb_time_read_cmpxchg(&t->bottom, e.bottom, s.bottom)) > + return false; > + return rb_time_read_cmpxchg(&t->end_cnt, e.end_cnt, s.end_cnt); > +} > + I have to think about this more, as I think there's a flaw in this cmpxchg algorithm. -- Steve