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 A157CC433E7 for ; Mon, 20 Jul 2020 15:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 765352065E for ; Mon, 20 Jul 2020 15:55:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595260515; bh=4ZY40wPsG4R+zjJrb68bpGinEpdKm4iPk7mTNF7io1k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=wb3NkfS4bCj0cXbG/VTsubqO1xSISxFJPONHB7fH6etv3jFDP6nOQd9k2THirBAx0 iO8e7FD5vk0e17jQfBwfSfOVAtY1D9BVHfLuRTFbqZGXO5cnvwhQZOKLeB40RYQBAT JtFVxNg7S4LhK2YW7Fa51fRIhNJYQVrnsCr0kA7M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731652AbgGTPzO (ORCPT ); Mon, 20 Jul 2020 11:55:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:54286 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730883AbgGTPzN (ORCPT ); Mon, 20 Jul 2020 11:55:13 -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 3D20922CF7; Mon, 20 Jul 2020 15:55:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595260512; bh=4ZY40wPsG4R+zjJrb68bpGinEpdKm4iPk7mTNF7io1k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TAXbPgCLymx4G2UpAKclXH6WBZRnXBifPNAcZchobD8lrwjRNGyCWqWuQhKD6Sgk1 eJRELOzCWjAJCZsUrCidNKCq8wY2sgmW1EpTaIfbMu4c/daKZz3FtnVMFz5a18uZgn sWFzoMYrVOwqUperUXiUOJXWpXc1k9WOvpQ2e/qg= 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 4.19 128/133] sched/fair: handle case of task_h_load() returning 0 Date: Mon, 20 Jul 2020 17:37:55 +0200 Message-Id: <20200720152809.917993544@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200720152803.732195882@linuxfoundation.org> References: <20200720152803.732195882@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7337,7 +7337,15 @@ static int detach_tasks(struct lb_env *e if (!can_migrate_task(p, env)) goto next; - 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) goto next;