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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 63FF4C4727E for ; Fri, 25 Sep 2020 21:26:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31E1E21D42 for ; Fri, 25 Sep 2020 21:26:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729117AbgIYV0o (ORCPT ); Fri, 25 Sep 2020 17:26:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:36122 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726149AbgIYV0n (ORCPT ); Fri, 25 Sep 2020 17:26:43 -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 2E25D21741; Fri, 25 Sep 2020 21:26:42 +0000 (UTC) Date: Fri, 25 Sep 2020 17:26:40 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Yafang Shao , Axel Rasmussen , Andrew Morton , Vlastimil Babka , Michel Lespinasse , Daniel Jordan , Davidlohr Bueso , Linux MM , Ingo Molnar , Joonsoo Kim , Mathieu Desnoyers Subject: Re: [PATCH 0/3 v2] tracing/mm: Add tracepoint_enabled() helper function for headers Message-ID: <20200925172640.701ca0a7@oasis.local.home> In-Reply-To: <20200925211206.423598568@goodmis.org> References: <20200925211206.423598568@goodmis.org> 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Bah, My cut-and-paste of my "quilt mail --send" chopped off Mathieu's email. Mathieu, I didn't meant to not Cc you on this. Do you need me to bounce the rest to you or you can get it from lore? -- Steve On Fri, 25 Sep 2020 17:12:06 -0400 Steven Rostedt wrote: > Tracepoints are not safe to be called directly from header files as they may > be included by C code that has CREATE_TRACE_POINTS defined, and this would > cause side effects and possibly break the build in hard to debug ways. Not > to mention it also will bloat the code being in commonly used inline > functions. > > Instead, it is recommended to call a tracepoint helper function that is > defined in a C file that calls the tracepoint. But we would only want this > function to be called if the tracepoint is enabled, as function calls add > overhead. > > The trace__enabled() function is also not safe to be called in a > header file as it is created by the tracepoint header, which suffers the > same fate if CREATE_TRACE_POINTS is defined. Instead, the tracepoint needs > to be declared as an extern, and the helper function can test the static key > to call the helper function that calls the tracepoint. > > This has been done by open coding the tracepoint extern and calling the > static key directly: > > commit 95813b8faa0cd ("mm/page_ref: add tracepoint to track down page reference manipulation") > commit 7f47d8cc039f ("x86, tracing, perf: Add trace point for MSR accesses") > > does this (back in 2015). Now we have another use case, so a helper function > should be created to keep the internals of the tracepoints from being spread > out in other subsystems. > > Link: https://lore.kernel.org/r/20200922125113.12ef1e03@gandalf.local.home > > This adds tracepoint_enabled() helper macro and DECLARE_TRACEPOINT() macro > to allow this to be done without exposing the internals of the tracepoints. > > The first patch adds the infrastructure, the second converts page_ref over > to it, and third converts over msr.h. > > Steven Rostedt (VMware) (3): > tracepoints: Add helper to test if tracepoint is enabled in a header > mm/page_ref: Convert the open coded tracepoint enabled to the new helper > x86: Use tracepoint_enabled() for msr tracepoints instead of open coding it > > ---- > > Changes since v1 (https://lore.kernel.org/r/20200924170928.466191266@goodmis.org): > > - Fixed using "trace_enabled()" instead of "tracepoint_enabled()" > (Mathieu Desnoyers reported) > > - Reworded to include comments about bloating the kernel when tracepoints > are used in commonly used inlined functions. > > - Added the msr update as well. > > > Documentation/trace/tracepoints.rst | 27 ++++++++++++++++++++++++ > arch/x86/include/asm/msr.h | 18 +++++++--------- > include/linux/page_ref.h | 42 ++++++++++++++++++------------------- > include/linux/tracepoint-defs.h | 34 ++++++++++++++++++++++++++++++ > 4 files changed, 90 insertions(+), 31 deletions(-)