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=-8.6 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 3E792C31E5C for ; Tue, 18 Jun 2019 03:13:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 140942084B for ; Tue, 18 Jun 2019 03:13:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="i/akO01k" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728283AbfFRDNH (ORCPT ); Mon, 17 Jun 2019 23:13:07 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:40572 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725829AbfFRDNH (ORCPT ); Mon, 17 Jun 2019 23:13:07 -0400 Received: by mail-pg1-f196.google.com with SMTP id w10so2206338pgj.7 for ; Mon, 17 Jun 2019 20:13:06 -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=KhfO2VsqXNYGGnbXV/fbIkGQmA6pJZHViPZUmbEm5iQ=; b=i/akO01kRXPc6Axn96IyXBj+YQCuHDqfJg2LW1VB5lHbMDJmoVsycyLyepIvadlC1Q jX/AJK9RmgOYlSW3gXqYbH9CetR3wj2KTUJpXIt5sAxILgz2FQ+Wy4cu/Yto4kGEXtTF nKDtP0sTyfrdBBfwrDflwYd4M08GmjUfImLgG0VlUZO7v0/4/r2lNH4Bk2LSOb4yeAfR rymBVV1U424Em9pVxi9XCbrMcV4EhwZ7s/YDdWW7k2pT4aqlWcGINf9YlNXjizODta3j mw3AFhRsKliEfqHkQ5zO5ed6hAxI9ZjT1HtJqN6bQqfKg5tYjuUHARqKbElqWBMvpq/P LPVg== 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=KhfO2VsqXNYGGnbXV/fbIkGQmA6pJZHViPZUmbEm5iQ=; b=l/ds31TtpNsrKhok4HjIK3xD6Ja/zguc/idSdVF5gxeC/c0IS3/nv/cWkMWIP7M1Zj ZMV08/ZTwR33r7YBT1K6+tp2/BjYoBiWe0Dk5IDKZHtYSegghiLQYQRl8FVb+XOzIkd3 L3my3+PLSsS3y4wfZk/Jn4hgilhdiG0idHu8rMK3keaEPK5wzYVc0S1dj7zQ2sEiCTRh M6QMwCeL3iark7/xTpgVlW2g/6esgAW5BbHB0Nx0FP1t6tZL6vkUA0d6l1RVUd5m2LFx 8UstO0IIF3X27w04m0/JfNbE9nwtcXFRpPjB7/o7yzQFvjRO7r82BZFbgrGXj3TX4UK1 aITg== X-Gm-Message-State: APjAAAUWNH9IV3c3Fe4uPmP5OzZKTtQyMlz2/g8lC9WzxvuUbSM2l2D9 UFJRaK20sdeE+oarfMtKDP7Iuhgr X-Google-Smtp-Source: APXvYqw+8b4cYPNCayrDZ1FsK4rjLmAl6pskm95IFxogKNcYD3SlVXwsRc62OXWDs15/b3EZhnWzMA== X-Received: by 2002:a17:90a:9bca:: with SMTP id b10mr2631153pjw.90.1560827586304; Mon, 17 Jun 2019 20:13:06 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.123]) by smtp.googlemail.com with ESMTPSA id d4sm608709pju.19.2019.06.17.20.13.04 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 17 Jun 2019 20:13:05 -0700 (PDT) From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , Ingo Molnar Subject: [PATCH] sched/nohz: Optimize get nohz timer target Date: Tue, 18 Jun 2019 11:13:01 +0800 Message-Id: <1560827581-8827-1-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, other 39 cpus 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. Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Wanpeng Li --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 83bd6bb..db550cf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -548,11 +548,12 @@ int get_nohz_timer_target(void) 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; } -- 2.7.4