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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 0D0D0C433DF for ; Wed, 26 Aug 2020 19:54:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA0D6207DF for ; Wed, 26 Aug 2020 19:54:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727124AbgHZTyB (ORCPT ); Wed, 26 Aug 2020 15:54:01 -0400 Received: from smtprelay0156.hostedemail.com ([216.40.44.156]:53306 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726798AbgHZTyB (ORCPT ); Wed, 26 Aug 2020 15:54:01 -0400 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay06.hostedemail.com (Postfix) with ESMTP id 40A721801BD68; Wed, 26 Aug 2020 19:54:00 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: elbow93_170ed9027067 X-Filterd-Recvd-Size: 2163 Received: from XPS-9350.home (unknown [47.151.133.149]) (Authenticated sender: joe@perches.com) by omf04.hostedemail.com (Postfix) with ESMTPA; Wed, 26 Aug 2020 19:53:58 +0000 (UTC) Message-ID: <9bfb4c4bd1415a8ce527a913730672508a8e8330.camel@perches.com> Subject: Re: [PATCH v3 2/2] dynamic debug: allow printing to trace event From: Joe Perches To: Steven Rostedt Cc: Vincent Whitchurch , jbaron@akamai.com, mingo@redhat.com, Nicolas Boichat , kernel@axis.com, corbet@lwn.net, pmladek@suse.com, sergey.senozhatsky@gmail.com, john.ogness@linutronix.de, linux-kernel@vger.kernel.org Date: Wed, 26 Aug 2020 12:53:57 -0700 In-Reply-To: <20200826153203.1a65c35d@oasis.local.home> References: <20200825153338.17061-1-vincent.whitchurch@axis.com> <20200825153338.17061-3-vincent.whitchurch@axis.com> <651f7ec449dfb28006bbc0b018d4f6e506bcda80.camel@perches.com> <20200826153203.1a65c35d@oasis.local.home> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.36.4-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2020-08-26 at 15:32 -0400, Steven Rostedt wrote: > On Tue, 25 Aug 2020 08:53:25 -0700 > Joe Perches wrote: > > > > The print buffer is statically allocated and managed using code borrowed > > > from __ftrace_trace_stack() and is limited to 256 bytes (four of these > > > are allocated per CPU to handle the various contexts); anything larger > > > will be truncated. > > > > There is an effort to avoid using trace_printk and the like > > so perhaps this feature should have the same compile time > > guard. > > No, this is fine for being in a production kernel. Basically, these are > simply debug printk()s that can also be put into the trace buffer. The > key difference to trace_printk() is that they are an event that needs > to be enabled to write into the buffer. It just seems like a backdoor way to convert various pr_debug functions (dev_dbg/netdev_dbg, et al) into tracing. What's the real value? Timing data? Something else?