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=-3.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no 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 879A2FA372C for ; Fri, 8 Nov 2019 13:21:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5EA2F20865 for ; Fri, 8 Nov 2019 13:21:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kkFUrzYf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729695AbfKHNVm (ORCPT ); Fri, 8 Nov 2019 08:21:42 -0500 Received: from merlin.infradead.org ([205.233.59.134]:44702 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729075AbfKHNVj (ORCPT ); Fri, 8 Nov 2019 08:21:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-Id:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=jgN3CjATcB8xdgDiKZbzkvUoJurgAK/0PjXwpC0hsm0=; b=kkFUrzYfceoVGz3pV13UB4D92q YBONRPl2gu1V3dUz4YdciUL/lk5GlHmjYOHBKUNywO/VsEJ+BocIfLqjC4NYGhcL3aimJmVFgtU0a 2WIrVbrXMlpaBDWgFANz67mtPdtVdXt4x39/G+1qiydPXJgUn26Ig0X7/7G0chDIh1EY/AfPQHaXe c03XSvW5DgpZRsFT7RM90SpP0/hT2R9XvjSxzi5iGGuMQoppQNuLeve7sXtJyH+OXQUwvZat1XeV6 jGBBsKVWcdDy8L3+0z1wkMoaYMWZYsLy/rXLD33z4S0O1oIDovO0eE67veKScR7vY4HUk9NZsSNWz yTgw0ltw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iT4CZ-0003ZS-As; Fri, 08 Nov 2019 13:21:24 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 591E2305FE7; Fri, 8 Nov 2019 14:20:15 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 43AFB2026E904; Fri, 8 Nov 2019 14:21:20 +0100 (CET) Message-Id: <20191108131909.488364308@infradead.org> User-Agent: quilt/0.65 Date: Fri, 08 Nov 2019 14:15:55 +0100 From: Peter Zijlstra To: mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de Cc: linux-kernel@vger.kernel.org, qperret@google.com, valentin.schneider@arm.com, qais.yousef@arm.com, ktkhai@virtuozzo.com, peterz@infradead.org Subject: [PATCH 2/7] sched/fair: Better document newidle_balance() References: <20191108131553.027892369@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Whilst chasing the pick_next_task() race, there was some confusion about the newidle_balance() return values. Document them. Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9920,6 +9920,11 @@ static inline void nohz_newidle_balance( /* * idle_balance is called by schedule() if this_cpu is about to become * idle. Attempts to pull tasks from other CPUs. + * + * Returns: + * <0 - we released the lock and there are !fair tasks present + * 0 - failed, no new tasks + * >0 - success, new (fair) tasks present */ int newidle_balance(struct rq *this_rq, struct rq_flags *rf) {