From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933043AbdHVOk3 (ORCPT ); Tue, 22 Aug 2017 10:40:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39251 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932894AbdHVOk1 (ORCPT ); Tue, 22 Aug 2017 10:40:27 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 9B3ACC0467CF 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] 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 16:40:24 +0200 Message-ID: <150341282404.1960.2812166781523027528.stgit@firesoul> 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 14:40:27 +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 1.6% 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 | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 486fd78eb8d5..56aa462760fa 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -208,12 +208,12 @@ static inline int get_recursion_context(int *recursion) { int rctx; - if (in_nmi()) - rctx = 3; + if (in_softirq()) + rctx = 1; else if (in_irq()) rctx = 2; - else if (in_softirq()) - rctx = 1; + else if (in_nmi()) + rctx = 3; else rctx = 0;