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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 98E08C2D0C2 for ; Fri, 3 Jan 2020 16:40:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7742E206E6 for ; Fri, 3 Jan 2020 16:40:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728062AbgACQkE (ORCPT ); Fri, 3 Jan 2020 11:40:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:46176 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727859AbgACQkD (ORCPT ); Fri, 3 Jan 2020 11:40:03 -0500 Received: from gandalf.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 A2E07206DB; Fri, 3 Jan 2020 16:40:02 +0000 (UTC) Date: Fri, 3 Jan 2020 11:40:01 -0500 From: Steven Rostedt To: "Frank A. Cancio Bello" Cc: Ingo Molnar , linux-kernel@vger.kernel.org, joel@joelfernandes.org, saiprakash.ranjan@codeaurora.org, nachukannan@gmail.com Subject: Re: [PATCH] tracing: Resets the trace buffer after a snapshot Message-ID: <20200103114001.2c118ab1@gandalf.local.home> In-Reply-To: <20191231085822.yxhph6wcguejb7al@frank-laptop> References: <20191231085822.yxhph6wcguejb7al@frank-laptop> 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 Tue, 31 Dec 2019 03:58:22 -0500 "Frank A. Cancio Bello" wrote: > Currently, when a snapshot is taken the trace_buffer and the > max_buffer are swapped. After this swap, the "new" trace_buffer is > not reset. This produces an odd behavior: after a snapshot is taken > the previous snapshot entries become available to the next reader of > the trace_buffer as far as the reading occurs before the buffer is > refilled with new entries by a writer. I consider this a feature not a bug ;-) Anyway, this behavior should be determined by an option. Care to create one? (reset_on_snapshot?) I would keep the default behavior the same, but document this a bit better. Thanks! -- Steve > > This patch resets the trace buffer after a snapshot is taken. > > Signed-off-by: Frank A. Cancio Bello > --- > > The following commands illustrate this odd behavior: > > # cd /sys/kernel/debug/tracing > # echo nop > current_tracer > # echo 1 > tracing_on > # echo m1 > trace_marker > # echo 1 > snapshot > # echo m2 > trace_marker > # echo 1 > snapshot > # cat trace > # tracer: nop > # > # entries-in-buffer/entries-written: 1/1 #P:2 > # > # _-----=> irqs-off > # / _----=> need-resched > # | / _---=> hardirq/softirq > # || / _--=> preempt-depth > # ||| / delay > # TASK-PID CPU# |||| TIMESTAMP FUNCTION > # | | | |||| | | > bash-550 [000] .... 50.479755: tracing_mark_write: m1 > > > kernel/trace/trace.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index ddb7e7f5fe8d..58373b5ae0cf 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -6867,10 +6867,13 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt, > break; > local_irq_disable(); > /* Now, we're going to swap */ > - if (iter->cpu_file == RING_BUFFER_ALL_CPUS) > + if (iter->cpu_file == RING_BUFFER_ALL_CPUS) { > update_max_tr(tr, current, smp_processor_id(), NULL); > - else > + tracing_reset_online_cpus(&tr->trace_buffer); > + } else { > update_max_tr_single(tr, current, iter->cpu_file); > + tracing_reset_cpu(&tr->trace_buffer, iter->cpu_file); > + } > local_irq_enable(); > break; > default: