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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 39B91C10F14 for ; Thu, 3 Oct 2019 17:42:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0EF4720830 for ; Thu, 3 Oct 2019 17:42:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570124546; bh=5u9Whsc6p/XfD9xIRZ6kTcBX2xjj+4JbTk+wCWZ59AA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=F5+yyt/p7fd024NfePeFfOTn9IxyxpdZxag5AeC+ZY4uhGR9I37wXDwsMMDfqXe9b zeY5BoKE7qhkhfm3Lw7lIPbV6M/RBbPV7RT9SXF0ajA2o6dhuY+zxxNvvTCZ0EJv93 a58pxAz0BzgUIzLSlsmQWRJksQU+iTqqSFBKqAAI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390463AbfJCRmY (ORCPT ); Thu, 3 Oct 2019 13:42:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:39716 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730924AbfJCP5W (ORCPT ); Thu, 3 Oct 2019 11:57:22 -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 30C5220830; Thu, 3 Oct 2019 15:57:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570118241; bh=5u9Whsc6p/XfD9xIRZ6kTcBX2xjj+4JbTk+wCWZ59AA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IGqME5eC9/Wb1MRfQfL+v3vLhoSqf0yP5Bc/6GZqbLUzq3Rl3399VF93s1an+KDgC kpaIv7RulDxaC5Puexa70c8mSP+6zi2CnALWLGe8/+EDfx6ymePbga3IyAPOGOWBBt Qk/NdkN1kTjaTfHAxvs008wPeHdMsL8cNb/734Fs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Guittot , "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.4 39/99] sched/fair: Fix imbalance due to CPU affinity Date: Thu, 3 Oct 2019 17:53:02 +0200 Message-Id: <20191003154314.415611606@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191003154252.297991283@linuxfoundation.org> References: <20191003154252.297991283@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 [ Upstream commit f6cad8df6b30a5d2bbbd2e698f74b4cafb9fb82b ] The load_balance() has a dedicated mecanism to detect when an imbalance is due to CPU affinity and must be handled at parent level. In this case, the imbalance field of the parent's sched_group is set. The description of sg_imbalanced() gives a typical example of two groups of 4 CPUs each and 4 tasks each with a cpumask covering 1 CPU of the first group and 3 CPUs of the second group. Something like: { 0 1 2 3 } { 4 5 6 7 } * * * * But the load_balance fails to fix this UC on my octo cores system made of 2 clusters of quad cores. Whereas the load_balance is able to detect that the imbalanced is due to CPU affinity, it fails to fix it because the imbalance field is cleared before letting parent level a chance to run. In fact, when the imbalance is detected, the load_balance reruns without the CPU with pinned tasks. But there is no other running tasks in the situation described above and everything looks balanced this time so the imbalance field is immediately cleared. The imbalance field should not be cleared if there is no other task to move when the imbalance is detected. Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/1561996022-28829-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 19d735ab44db4..cd2fb8384fbe3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7313,9 +7313,10 @@ static int load_balance(int this_cpu, struct rq *this_rq, out_balanced: /* * We reach balance although we may have faced some affinity - * constraints. Clear the imbalance flag if it was set. + * constraints. Clear the imbalance flag only if other tasks got + * a chance to move and fix the imbalance. */ - if (sd_parent) { + if (sd_parent && !(env.flags & LBF_ALL_PINNED)) { int *group_imbalance = &sd_parent->groups->sgc->imbalance; if (*group_imbalance) -- 2.20.1