From patchwork Fri Sep 25 21:12:07 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 11800777 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5881B6CA for ; Fri, 25 Sep 2020 21:18:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DE9B923730 for ; Fri, 25 Sep 2020 21:18:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DE9B923730 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 454076B0072; Fri, 25 Sep 2020 17:18:24 -0400 (EDT) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id DACC76B0070; Fri, 25 Sep 2020 17:18:23 -0400 (EDT) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BAE716B006E; Fri, 25 Sep 2020 17:18:23 -0400 (EDT) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0103.hostedemail.com [216.40.44.103]) by kanga.kvack.org (Postfix) with ESMTP id 9B1CF6B006E for ; Fri, 25 Sep 2020 17:18:23 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 60B17181AE862 for ; Fri, 25 Sep 2020 21:18:23 +0000 (UTC) X-FDA: 77302847286.24.brass26_0e11b682716a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 44DFD1A4A0 for ; Fri, 25 Sep 2020 21:18:23 +0000 (UTC) X-Spam-Summary: 1,0,0,2f80f377713749dc,d41d8cd98f00b204,srs0=yqgo=dc=goodmis.org=rostedt@kernel.org,,RULES_HIT:41:152:355:379:800:901:960:967:973:988:989:1183:1260:1263:1277:1313:1314:1345:1434:1437:1516:1518:1535:1544:1593:1594:1605:1711:1730:1747:1777:1792:1801:2194:2199:2393:2525:2553:2559:2565:2682:2685:2693:2859:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3657:3770:3865:3866:3867:3868:3870:3871:3872:3873:3874:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4321:4605:5007:6119:6261:6755:7266:7576:7903:7904:8660:8985:9025:9388:10004:11026:11232:11473:11658:11914:12043:12219:12291:12296:12297:12438:12517:12519:12555:12895:12986:13148:13230:13255:14181:14394:14659:14721:21080:21451:21627:21740:21781:21939:21966:30029:30041:30054:30070:30074:30090,0,RBL:198.145.29.99:@kernel.org:.lbl8.mailshell.net-64.100.201.201 62.2.0.100;04yrj7mrrz64qnf9kiwcyw3mxykbhocxnctumma4n9rzmofeh3wuihau1xpwuc5.y49rkcz4m5r484yrhx7nfs18nq9bwb3yhjqa9w5hr45r8roy9g9hhg645shbhg f.g-lbl8 X-HE-Tag: brass26_0e11b682716a X-Filterd-Recvd-Size: 5447 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Fri, 25 Sep 2020 21:18:22 +0000 (UTC) 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 87328221EC; Fri, 25 Sep 2020 21:18:21 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.94) (envelope-from ) id 1kLv6h-002CtJ-SY; Fri, 25 Sep 2020 17:18:19 -0400 Message-ID: <20200925211819.767526657@goodmis.org> User-Agent: quilt/0.66 Date: Fri, 25 Sep 2020 17:12:07 -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 Subject: [PATCH 1/3 v2] tracepoints: Add helper to test if tracepoint is enabled in a header References: <20200925211206.423598568@goodmis.org> MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: "Steven Rostedt (VMware)" As tracepoints are discouraged from being added in a header because it can cause side effects if other tracepoints are in headers, as well as bloat the kernel as the trace_() function is not a small inline, the common workaround is to add a function call that calls a wrapper function in a C file that then calls the tracepoint. But as function calls add overhead, this function should only be called when the tracepoint in question is enabled. To get around this overhead, a static_branch can be used to only have the tracepoint wrapper get called when the tracepoint is enabled. Add a tracepoint_enabled(tp) macro that gets passed the name of the tracepoint, and this becomes a static_branch that is enabled when the tracepoint is enabled and is a nop when the tracepoint is disabled. Signed-off-by: Steven Rostedt (VMware) Acked-by: Vlastimil Babka --- Documentation/trace/tracepoints.rst | 27 +++++++++++++++++++++++ include/linux/tracepoint-defs.h | 34 +++++++++++++++++++++++++++++ 2 files changed, 61 insertions(+) diff --git a/Documentation/trace/tracepoints.rst b/Documentation/trace/tracepoints.rst index 6e3ce3bf3593..68579ebd1e4c 100644 --- a/Documentation/trace/tracepoints.rst +++ b/Documentation/trace/tracepoints.rst @@ -146,3 +146,30 @@ with jump labels and avoid conditional branches. define tracepoints. Check http://lwn.net/Articles/379903, http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362 for a series of articles with more details. + +If you require calling a tracepoint from a header file, it is not +recommended to call one directly or to use the trace__enabled() +function call, as tracepoints in header files can have side effects if a +header is included from a file that has CREATE_TRACE_POINTS set, as +well as the trace_() is not that small of an inline +and can bloat the kernel if used by other inlined functions. Instead, +include tracepoint-defs.h and use tracepoint_enabled(). + +In a C file:: + + void do_trace_foo_bar_wrapper(args) + { + trace_foo_bar(args); + } + +In the header file:: + + DECLEARE_TRACEPOINT(foo_bar); + + static inline void some_inline_function() + { + [..] + if (tracepoint_enabled(foo_bar)) + do_trace_foo_bar_wrapper(args); + [..] + } diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h index b29950a19205..60625973faaf 100644 --- a/include/linux/tracepoint-defs.h +++ b/include/linux/tracepoint-defs.h @@ -48,4 +48,38 @@ struct bpf_raw_event_map { u32 writable_size; } __aligned(32); +/* + * If a tracepoint needs to be called from a header file, it is not + * recommended to call it directly, as tracepoints in header files + * may cause side-effects and bloat the kernel. Instead, use + * tracepoint_enabled() to test if the tracepoint is enabled, then if + * it is, call a wrapper function defined in a C file that will then + * call the tracepoint. + * + * For "trace_foo_bar()", you would need to create a wrapper function + * in a C file to call trace_foo_bar(): + * void do_trace_foo_bar(args) { trace_foo_bar(args); } + * Then in the header file, declare the tracepoint: + * DECLARE_TRACEPOINT(foo_bar); + * And call your wrapper: + * static inline void some_inlined_function() { + * [..] + * if (tracepoint_enabled(foo_bar)) + * do_trace_foo_bar(args); + * [..] + * } + * + * Note: tracepoint_enabled(foo_bar) is equivalent to trace_foo_bar_enabled() + * but is safe to have in headers, where trace_foo_bar_enabled() is not. + */ +#define DECLARE_TRACEPOINT(tp) \ + extern struct tracepoint __tracepoint_##tp + +#ifdef CONFIG_TRACEPOINTS +# define tracepoint_enabled(tp) \ + static_key_false(&(__tracepoint_##tp).key) +#else +# define tracepoint_enabled(tracepoint) false +#endif + #endif