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=-9.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 82928C4321A for ; Fri, 28 Jun 2019 00:43:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 526AC2086D for ; Fri, 28 Jun 2019 00:43:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="upp295eE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726671AbfF1AnU (ORCPT ); Thu, 27 Jun 2019 20:43:20 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:34824 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726579AbfF1AnT (ORCPT ); Thu, 27 Jun 2019 20:43:19 -0400 Received: by mail-pl1-f193.google.com with SMTP id w24so2203721plp.2 for ; Thu, 27 Jun 2019 17:43:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=XK5NFZh7pG1K+u3GPFcGObWPOefyWYFPM8I5XfkBG/8=; b=upp295eE4zrZ2rfDBy6cAlytz9+pNGthZTHLKTr1OO9dTOiMZf6JwjuEq8ekcHwklm cZv7vb8Oym6r76qlAR2DGFlE+Fbgscpula7GgOLKLeBbiFxjKOlKf23bv6QUIvRVWaHE Ea+r/DyVrIdjoJq+E65Gw199EVyBXO2RUkgTDAb6ac+RO8yV6feWGc6NCWESOj4QnZ+6 wxVgJDAGElxaJAHNExlL90/amJQsDPcePEhhadmUwuhv9YNJvTpqQWp/tp7mCG/2hSjS b/Zb6zy2r9GhjEZ8w8H3xBiCMMbqthMSoge28/XS+uZd9P1/BJZP4YQ0MGL2gbG8GElv DoPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=XK5NFZh7pG1K+u3GPFcGObWPOefyWYFPM8I5XfkBG/8=; b=pCYNhtpDZmyG2w8gicLTFCqtROKa95I27aTD4QS2QGf9KstgohyIET0V/EsruKZuqk MEUItpRa9GSdpt4Oq5AKlhe5/OjRTk9kMAp7+Yc+qXRak4WoBNiWMuZ0L5ZYpdDuI2aJ Rm9AIOQJexnjtCi8fMs7+/jMGFtmSO8pB4736S1sUDEr4riaPFtA6RYzs4RMZvEIKmeZ j8IIRmCF3R6OS+noOM0tV2QJhYpaSCN2HUbCrDLkzIabEwXUuyfE+GrA2Uzr+m5Tx9tG Bc60dGOVYHXM8x32W7fHC3iHQ/xHw6yASWnpGSDr+LeeuGZAMng+WiIQ8TJTVvK+sTNr 5dTQ== X-Gm-Message-State: APjAAAV5GUlN1XThNezL0Ll1uJLEJOnmX2YA7kvulCQYLeBYQ5OZE6nP Ocz/z0AkOXzP++Z1rKPaR2fbpfclEj4= X-Google-Smtp-Source: APXvYqxegHsYVbbcs7Qa6pW5xQvySaMtUe0xaNM73KyiAwlrJT2OfQixsRUUai9jwK7wPOKdbdO+NA== X-Received: by 2002:a17:902:7b84:: with SMTP id w4mr7879007pll.22.1561682598960; Thu, 27 Jun 2019 17:43:18 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.123]) by smtp.googlemail.com with ESMTPSA id n89sm11927802pjc.0.2019.06.27.17.43.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 27 Jun 2019 17:43:18 -0700 (PDT) From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , Ingo Molnar , Frederic Weisbecker , Thomas Gleixner Subject: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() Date: Fri, 28 Jun 2019 08:43:12 +0800 Message-Id: <1561682593-12071-1-git-send-email-wanpengli@tencent.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li On a machine, cpu 0 is used for housekeeping, the other 39 cpus in the same socket are in nohz_full mode. We can observe huge time burn in the loop for seaching nearest busy housekeeper cpu by ftrace. 2) | get_nohz_timer_target() { 2) 0.240 us | housekeeping_test_cpu(); 2) 0.458 us | housekeeping_test_cpu(); ... 2) 0.292 us | housekeeping_test_cpu(); 2) 0.240 us | housekeeping_test_cpu(); 2) 0.227 us | housekeeping_any_cpu(); 2) + 43.460 us | } This patch optimizes the searching logic by finding a nearest housekeeper cpu in the housekeeping cpumask, it can minimize the worst searching time from ~44us to < 10us in my testing. In addition, the last iterated busy housekeeper can become a random candidate while current CPU is a better fallback if it is a housekeeper. Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Frederic Weisbecker Cc: Thomas Gleixner Signed-off-by: Wanpeng Li --- v1 -> v2: * current CPU is a better fallback if it is a housekeeper kernel/sched/core.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 102dfcf..04a0f6a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -539,27 +539,32 @@ void resched_cpu(int cpu) */ int get_nohz_timer_target(void) { - int i, cpu = smp_processor_id(); + int i, cpu = smp_processor_id(), default_cpu = -1; struct sched_domain *sd; - if (!idle_cpu(cpu) && housekeeping_cpu(cpu, HK_FLAG_TIMER)) - return cpu; + if (housekeeping_cpu(cpu, HK_FLAG_TIMER)) { + if (!idle_cpu(cpu)) + return cpu; + default_cpu = cpu; + } rcu_read_lock(); for_each_domain(cpu, sd) { - for_each_cpu(i, sched_domain_span(sd)) { + for_each_cpu_and(i, sched_domain_span(sd), + housekeeping_cpumask(HK_FLAG_TIMER)) { if (cpu == i) continue; - if (!idle_cpu(i) && housekeeping_cpu(i, HK_FLAG_TIMER)) { + if (!idle_cpu(i)) { cpu = i; goto unlock; } } } - if (!housekeeping_cpu(cpu, HK_FLAG_TIMER)) - cpu = housekeeping_any_cpu(HK_FLAG_TIMER); + if (default_cpu == -1) + default_cpu = housekeeping_any_cpu(HK_FLAG_TIMER); + cpu = default_cpu; unlock: rcu_read_unlock(); return cpu; -- 1.8.3.1