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=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 ABC16C433FC for ; Mon, 20 Jul 2020 16:15:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83E6D2064B for ; Mon, 20 Jul 2020 16:15:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595261729; bh=JPEzLH6tKL+WMDuIPV6rnfvXsiGH+MU8f5d/RrU/mdU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vheuBElmuNlGgIsMZUamqGINwNMbsRSPFUZAl5NqjcSFnVmQs/mqhQqo2+75bUSCH WjW/DWJE2O2T+2tHbm2dbHquEP9VtC9nBGdHA57xzEPsTZLQBHF32yqyr9DShwyk5S dE14ypc/4UnWSY5Iw8wJInO1C11e04MGlJLjimJ8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388416AbgGTQP2 (ORCPT ); Mon, 20 Jul 2020 12:15:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:56284 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388410AbgGTQPZ (ORCPT ); Mon, 20 Jul 2020 12:15:25 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 52CDF20656; Mon, 20 Jul 2020 16:15:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595261724; bh=JPEzLH6tKL+WMDuIPV6rnfvXsiGH+MU8f5d/RrU/mdU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jV6qWQxJjbtpWQxUffQXqYE0HJkIZse2luGdK5apWavP772u1YGdu7/7EOqbzdqAG yTaRFlfEE2nNuCdYpBUs2d76uDyYWxqwA07jUXcSEjQxZKal5F/VqpRNUccHBKDxrh zE/u5kEFhjqCx5c9qa/pOwnXL8CJUBw4DPsY0Ir8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Guittot , "Peter Zijlstra (Intel)" , Valentin Schneider , Dietmar Eggemann Subject: [PATCH 5.7 220/244] sched/fair: handle case of task_h_load() returning 0 Date: Mon, 20 Jul 2020 17:38:11 +0200 Message-Id: <20200720152836.312927779@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200720152825.863040590@linuxfoundation.org> References: <20200720152825.863040590@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vincent Guittot commit 01cfcde9c26d8555f0e6e9aea9d6049f87683998 upstream. task_h_load() can return 0 in some situations like running stress-ng mmapfork, which forks thousands of threads, in a sched group on a 224 cores system. The load balance doesn't handle this correctly because env->imbalance never decreases and it will stop pulling tasks only after reaching loop_max, which can be equal to the number of running tasks of the cfs. Make sure that imbalance will be decreased by at least 1. misfit task is the other feature that doesn't handle correctly such situation although it's probably more difficult to face the problem because of the smaller number of CPUs and running tasks on heterogenous system. We can't simply ensure that task_h_load() returns at least one because it would imply to handle underflow in other places. Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Dietmar Eggemann Tested-by: Dietmar Eggemann Cc: # v4.4+ Link: https://lkml.kernel.org/r/20200710152426.16981-1-vincent.guittot@linaro.org Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4033,7 +4033,11 @@ static inline void update_misfit_status( return; } - rq->misfit_task_load = task_h_load(p); + /* + * Make sure that misfit_task_load will not be null even if + * task_h_load() returns 0. + */ + rq->misfit_task_load = max_t(unsigned long, task_h_load(p), 1); } #else /* CONFIG_SMP */ @@ -7633,7 +7637,14 @@ static int detach_tasks(struct lb_env *e switch (env->migration_type) { case migrate_load: - load = task_h_load(p); + /* + * Depending of the number of CPUs and tasks and the + * cgroup hierarchy, task_h_load() can return a null + * value. Make sure that env->imbalance decreases + * otherwise detach_tasks() will stop only after + * detaching up to loop_max tasks. + */ + load = max_t(unsigned long, task_h_load(p), 1); if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)