From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751657AbdHVRWs (ORCPT ); Tue, 22 Aug 2017 13:22:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52187 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751244AbdHVRWr (ORCPT ); Tue, 22 Aug 2017 13:22:47 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 905C6C014161 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=brouer@redhat.com Subject: [PATCH V2] trace: adjust code layout in get_recursion_context From: Jesper Dangaard Brouer To: Arnaldo Carvalho de Melo Cc: Peter Zijlstra , Jesper Dangaard Brouer , linux-kernel@vger.kernel.org, Jiri Olsa , Ingo Molnar Date: Tue, 22 Aug 2017 19:22:43 +0200 Message-ID: <150342256382.16595.986861478681783732.stgit@firesoul> In-Reply-To: <20170822191037.286e70ab@redhat.com> References: <20170822191037.286e70ab@redhat.com> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Tue, 22 Aug 2017 17:22:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In an XDP redirect applications using tracepoint xdp:xdp_redirect to diagnose TX overrun, I noticed perf_swevent_get_recursion_context() was consuming 2% CPU. This was reduced to 1.85% with this simple change. Looking at the annotated asm code, it was clear that the unlikely case in_nmi() test was chosen (by the compiler) as the most likely event/branch. This small adjustment makes the compiler (gcc version 7.1.1 20170622 (Red Hat 7.1.1-3)) put in_nmi() as an unlikely branch. Signed-off-by: Jesper Dangaard Brouer --- kernel/events/internal.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 486fd78eb8d5..e1a7ac7bd686 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -208,7 +208,7 @@ static inline int get_recursion_context(int *recursion) { int rctx; - if (in_nmi()) + if (unlikely(in_nmi())) rctx = 3; else if (in_irq()) rctx = 2;