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=-2.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 4790CC04AB1 for ; Thu, 9 May 2019 18:45:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24E8221848 for ; Thu, 9 May 2019 18:45:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727392AbfEISpk (ORCPT ); Thu, 9 May 2019 14:45:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38368 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726892AbfEISpg (ORCPT ); Thu, 9 May 2019 14:45:36 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 14F547DCC1; Thu, 9 May 2019 18:45:36 +0000 (UTC) Received: from treble (ovpn-123-166.rdu2.redhat.com [10.10.123.166]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B130F4A3; Thu, 9 May 2019 18:45:33 +0000 (UTC) Date: Thu, 9 May 2019 13:45:31 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: Linus Torvalds , David Laight , Peter Zijlstra , "tglx@linutronix.de" , "hpa@zytor.com" , "julien.thierry@arm.com" , "will.deacon@arm.com" , "luto@amacapital.net" , "mingo@kernel.org" , "catalin.marinas@arm.com" , "james.morse@arm.com" , "valentin.schneider@arm.com" , "brgerst@gmail.com" , "luto@kernel.org" , "bp@alien8.de" , "dvlasenk@redhat.com" , "linux-kernel@vger.kernel.org" , "dvyukov@google.com" Subject: Re: [PATCH 02/25] tracing: Improve "if" macro code generation Message-ID: <20190509184531.jhinxi2x2pdfaefb@treble> References: <20190318153840.906404905@infradead.org> <20190318155140.058627431@infradead.org> <20190509090058.6554dc81@gandalf.local.home> <20190509142902.08a32f20@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190509142902.08a32f20@gandalf.local.home> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 09 May 2019 18:45:36 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 09, 2019 at 02:29:02PM -0400, Steven Rostedt wrote: > On Thu, 9 May 2019 09:51:59 -0700 > Linus Torvalds wrote: > > > On Thu, May 9, 2019 at 6:01 AM Steven Rostedt wrote: > > > > > > This patch works. Can I get your Signed-off-by for it? > > > > Yes. Please write some kind of comprehensible commit log for it, but > > How's this: > > "Peter Zijlstra noticed that with CONFIG_PROFILE_ALL_BRANCHES, the "if" > macro converts the conditional to an array index. This can cause GCC > to create horrible code. When there are nested ifs, the generated code > uses register values to encode branching decisions. > > Josh Poimboeuf found that replacing the define "if" macro from using > the condition as an array index and incrementing the branch statics > with an if statement itself, reduced the asm complexity and shrinks the > generated code quite a bit. > > But this can be simplified even further by replacing the internal if > statement with a ternary operator. > > Reported-by: Peter Zijlstra (Intel) > Reported-by: Josh Poimboeuf Actually, my original fix already went in: 37686b1353cf ("tracing: Improve "if" macro code generation") But it introduced a regression: https://lkml.kernel.org/r/201905040509.iqQ2CrOU%lkp@intel.com which Linus' patch fixes for some reason. -- Josh