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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 CA469C282CA for ; Wed, 13 Feb 2019 06:50:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1F79222BE for ; Wed, 13 Feb 2019 06:50:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387445AbfBMGuF (ORCPT ); Wed, 13 Feb 2019 01:50:05 -0500 Received: from mailgw02.mediatek.com ([210.61.82.184]:15466 "EHLO mailgw02.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S2387415AbfBMGuE (ORCPT ); Wed, 13 Feb 2019 01:50:04 -0500 X-UUID: 621f949198ff4ac497ea4337c4f676c0-20190213 X-UUID: 621f949198ff4ac497ea4337c4f676c0-20190213 Received: from mtkexhb01.mediatek.inc [(172.21.101.102)] by mailgw02.mediatek.com (envelope-from ) (mhqrelay.mediatek.com ESMTP with TLS) with ESMTP id 1942036351; Wed, 13 Feb 2019 14:49:46 +0800 Received: from mtkcas07.mediatek.inc (172.21.101.84) by mtkmbs03n1.mediatek.inc (172.21.101.181) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 13 Feb 2019 14:49:45 +0800 Received: from [172.21.77.33] (172.21.77.33) by mtkcas07.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Wed, 13 Feb 2019 14:49:45 +0800 Message-ID: <1550040585.12645.9.camel@mtkswgap22> Subject: Re: [PATCH 1/1] tracing: Fix event_trace_printk loss on printk_format. From: Mars Cheng To: Steven Rostedt CC: Andress Kuo , CC Hwang , , , Date: Wed, 13 Feb 2019 14:49:45 +0800 In-Reply-To: <1550033650.7648.2.camel@mtkswgap22> References: <1549971717-4693-1-git-send-email-mars.cheng@mediatek.com> <20190212204113.5ecaa2a1@gandalf.local.home> <1550033650.7648.2.camel@mtkswgap22> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve On Wed, 2019-02-13 at 12:54 +0800, Mars Cheng wrote: > Hi Steve > > On Tue, 2019-02-12 at 20:41 -0500, Steven Rostedt wrote: > > On Tue, 12 Feb 2019 19:41:57 +0800 > > Mars Cheng wrote: > > > > > From: Andress Kuo > > > > > > If fmt on event_trace_printk is not a constant, It means that something not > > > guaranteed, so the compiler optimizes the fmt out, and then the > > > __trace_printk_fmt section is not filled. if __trace_printk_fmt is not > > > filled, the kernel will not allocate the special buffers needed for the > > > event_trace_printk() and then not shown in the file output > > > sys/kernel/debug/tracing/print_formats. > > > > > > Adding a "__used" to the variable in the __trace_printk_fmt section on > > > event_trace_printk() will keep it around, even though it is set to NULL. > > > This will keep the string from being printed in the > > > sys/kernel/debug/tracing/printk_formats section. > > > > > > We can also refer to commit 3debb0a9ddb1 ("tracing: Fix trace_printk() > > > to print when not using bprintk()")that it had similar issue on path of > > > trace_printk(). > > > > Honestly, I don't even remember why that macro was created. I think > > it's a remnant from the creation of the trace events. I think the best > > solution is just to nuke it. It shouldn't be used anymore. > > > > I'll dig a bit deeper into the history of that macro, but I'm thinking > > it shouldn't exist anymore. > > > > [ /me returns from walking down memory lane ] > > > > Wow, that brings back some wild memories. Yes, that macro must die, and > > I wish the history of it could die along with it ;-) The horror of the > > old ways I tell you. The event_trace_printk() was the original way we > > displayed events! No real formatting, no parsing my userspace tools. It > > was just a glamorized printk. It was called TRACE_FORMAT() which was > > deprecated by today's TRACE_EVENT(). > > > > That macro should have been removed by commit b8e65554d80b4. > > > > Please just send a patch to delete that macro. Let's not be maintaining > > it. It gives me nightmares. > > > > -- Steve > > Got it, I will send another patch to remove the nightmares. :-) > > Thanks. After some grep, I found event_trace_printk() not used in 5.0-rc*. But trace_printk() is still used in several places. kernel/trace/ring_buffer_benchmark.c:415: trace_printk("Sleeping for 10 secs\n"); ... drivers/gpu/drm/i915/i915_gem.h:66:#define GEM_TRACE(...) trace_printk(__VA_ARGS__) drivers/hwtracing/stm/dummy_stm.c:30: trace_printk("[%u:%u] [pkt: %x/% x] (%llx)\n", master, channel, ... since they are similar functions, do you prefer remove both of them or just remove event_trace_printk()? the former approach might affect some modules, and the latter approach keeps nightmares, right? Thanks. >