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 C9313C433E3 for ; Fri, 21 Aug 2020 08:48:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0FFF21741 for ; Fri, 21 Aug 2020 08:48:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728114AbgHUIsN convert rfc822-to-8bit (ORCPT ); Fri, 21 Aug 2020 04:48:13 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:60563 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728109AbgHUIsL (ORCPT ); Fri, 21 Aug 2020 04:48:11 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-223-9puSzk3tPJqiaeE2oL8ASg-1; Fri, 21 Aug 2020 09:48:07 +0100 X-MC-Unique: 9puSzk3tPJqiaeE2oL8ASg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 21 Aug 2020 09:48:06 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 21 Aug 2020 09:48:06 +0100 From: David Laight To: 'Steven Rostedt' , Nicolas Boichat CC: Mauro Carvalho Chehab , Greg Kroah-Hartman , Andy Shevchenko , Sakari Ailus , "devel@driverdev.osuosl.org" , lkml , "Linux Media Mailing List" , Peter Zijlstra , Thomas Gleixner , Josh Poimboeuf Subject: RE: [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed Thread-Topic: [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed Thread-Index: AQHWd1MRQFeXK2GIIEihfK8khxWsrqlCP3rw Date: Fri, 21 Aug 2020 08:48:05 +0000 Message-ID: <21fae92da07c4566ba4eed3b5e1bce2d@AcuMS.aculab.com> References: <20200820170951.v4.1.Ia54fe801f246a0b0aee36fb1f3bfb0922a8842b0@changeid> <20200820170951.v4.3.I066d89f39023956c47fb0a42edf196b3950ffbf7@changeid> <20200820102347.15d2f610@oasis.local.home> <20200820203601.4f70bf98@oasis.local.home> In-Reply-To: <20200820203601.4f70bf98@oasis.local.home> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org From: Steven Rostedt > Sent: 21 August 2020 01:36 > On Fri, 21 Aug 2020 08:13:00 +0800 > Nicolas Boichat wrote: > > > On Thu, Aug 20, 2020 at 10:23 PM Steven Rostedt wrote: > > > > > > On Thu, 20 Aug 2020 17:14:12 +0800 > > > Nicolas Boichat wrote: > > > > > > > Technically, we could only initialize the trace_printk buffers > > > > when the print env is switched, to avoid the build error and > > > > unconditional boot-time warning, but I assume this printing > > > > framework will eventually get removed when the driver moves out > > > > of staging? > > > > > > Perhaps this should be converting into a trace event. Look at what bpf > > > did for their bpf_trace_printk(). > > > > > > The more I think about it, the less I like this series. > > > > To make it clear, the primary goal of this series is to get rid of > > trace_printk sprinkled in the kernel by making sure some randconfig > > builds fail. Since my v2, there already has been one more added (the > > one that this patch removes), so I'd like to land 2/3 ASAP to prevent > > even more from being added. > > > > Looking at your reply on 1/3, I think we are aligned on that goal? Is > > there some other approach you'd recommend? > > > > Now, I'm not pretending my fixes are the best possible ones, but I > > would much rather have the burden of converting to trace events on the > > respective driver maintainers. (btw is there a short > > documentation/tutorial that I could link to in these patches, to help > > developers understand what is the recommended way now?) > > > > I like the goal, but I guess I never articulated the problem I have > with the methodology. > > trace_printk() is meant to be a debugging tool. Something that people > can and do sprinkle all over the kernel to help them find a bug in > areas that are called quite often (where printk() is way too slow). > > The last thing I want them to deal with is adding a trace_printk() with > their distro's config (or a config from someone that triggered the bug) > only to have the build to fail, because they also need to add a config > value. > > I add to the Cc a few developers I know that use trace_printk() in this > fashion. I'd like to hear their view on having to add a config option > to make trace_printk work before they test a config that is sent to > them. Is it worth having three compile-time options: 1) trace_printk() ignored. 2) trace_printk() enabled. 3) trace_printk() generates a compile time error. Normal kernel builds would ignore calls. Either a config option or a module option (etc) would enable it. A config option that 'rand-config' builds would turn on would generate compile-time errors. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)