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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 60C56C32792 for ; Thu, 3 Oct 2019 20:36:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D7D52070B for ; Thu, 3 Oct 2019 20:36:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732900AbfJCUgQ (ORCPT ); Thu, 3 Oct 2019 16:36:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38706 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726669AbfJCUgQ (ORCPT ); Thu, 3 Oct 2019 16:36:16 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3A320898106; Thu, 3 Oct 2019 20:36:16 +0000 (UTC) Received: from llong.com (ovpn-122-104.rdu2.redhat.com [10.10.122.104]) by smtp.corp.redhat.com (Postfix) with ESMTP id CB65719C69; Thu, 3 Oct 2019 20:36:12 +0000 (UTC) From: Waiman Long To: Ingo Molnar , "Peter Zijlstra (Intel)" , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , Sebastian Andrzej Siewior , Juri Lelli , Waiman Long Subject: [PATCH v2] lib/smp_processor_id: Don't use cpumask_equal() Date: Thu, 3 Oct 2019 16:36:08 -0400 Message-Id: <20191003203608.21881-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.67]); Thu, 03 Oct 2019 20:36:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The check_preemption_disabled() function uses cpumask_equal() to see if the task is bounded to the current CPU only. cpumask_equal() calls memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP, the slow memcmp() function in lib/string.c is used. On a RT kernel that call check_preemption_disabled() very frequently, below is the perf-record output of a certain microbenchmark: 42.75% 2.45% testpmd [kernel.kallsyms] [k] check_preemption_disabled 40.01% 39.97% testpmd [kernel.kallsyms] [k] memcmp We should avoid calling memcmp() in performance critical path. So the cpumask_equal() call is now replaced with an equivalent simpler check. Signed-off-by: Waiman Long --- lib/smp_processor_id.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c index 60ba93fc42ce..bd9571653288 100644 --- a/lib/smp_processor_id.c +++ b/lib/smp_processor_id.c @@ -23,7 +23,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2) * Kernel threads bound to a single CPU can safely use * smp_processor_id(): */ - if (cpumask_equal(current->cpus_ptr, cpumask_of(this_cpu))) + if (current->nr_cpus_allowed == 1) goto out; /* -- 2.18.1