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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,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 0E604C43381 for ; Mon, 18 Mar 2019 17:41:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC49320989 for ; Mon, 18 Mar 2019 17:41:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727847AbfCRRlz (ORCPT ); Mon, 18 Mar 2019 13:41:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:57202 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726860AbfCRRly (ORCPT ); Mon, 18 Mar 2019 13:41:54 -0400 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 D6AB32070D; Mon, 18 Mar 2019 17:41:52 +0000 (UTC) Date: Mon, 18 Mar 2019 13:41:51 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: torvalds@linux-foundation.org, 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, jpoimboe@redhat.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: <20190318134151.4398b2e2@gandalf.local.home> In-Reply-To: <20190318155140.058627431@infradead.org> References: <20190318153840.906404905@infradead.org> <20190318155140.058627431@infradead.org> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 18 Mar 2019 16:38:42 +0100 Peter Zijlstra wrote: > 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. > > Make it easier for GCC to optimize by keeping the conditional as a > conditional rather than converting it to an integer. This shrinks the > generated code quite a bit, and also makes the code sane enough for > objtool to understand. > > Cc: rostedt@goodmis.org > Cc: valentin.schneider@arm.com > Cc: luto@amacapital.net > Cc: brgerst@gmail.com > Cc: catalin.marinas@arm.com > Cc: mingo@kernel.org > Cc: dvlasenk@redhat.com > Cc: will.deacon@arm.com > Cc: julien.thierry@arm.com > Cc: torvalds@linux-foundation.org > Cc: dvyukov@google.com > Cc: bp@alien8.de > Cc: tglx@linutronix.de > Cc: james.morse@arm.com > Cc: luto@kernel.org > Cc: hpa@zytor.com > Reported-by: Peter Zijlstra > Signed-off-by: Josh Poimboeuf > Signed-off-by: Peter Zijlstra (Intel) Acked-by: Steven Rostedt (VMware) -- Steve > Link: https://lkml.kernel.org/r/20190307174802.46fmpysxyo35hh43@treble > --- > include/linux/compiler.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_ > .line = __LINE__, \ > }; \ > ______r = !!(cond); \ > - ______f.miss_hit[______r]++; \ > + ______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\ > ______r; \ > })) > #endif /* CONFIG_PROFILE_ALL_BRANCHES */ >