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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 AA91CC3A5A6 for ; Sun, 22 Sep 2019 19:29:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79F1F206B6 for ; Sun, 22 Sep 2019 19:29:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569180553; bh=VR7Qr2sSZDvvWUGGowSu7a6WGDqx1uqcGdlqRG8+qwM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=GY9L8OsDnVbo1HVVeakvVVLxxCOtkjB0THPtTN0tw2Nw4e20Dy6RqpSnjXwrZGSc8 KNuBCdPV6Udsepvs7HN5jWQH/gT0+gPc1kzgG8qqRgFMkCLWJ5rjIC8g70zu9HWws0 exGKhZwcAlqDtp8GifYGW9q9IsdS2PqeF78oJAB0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392894AbfIVSuT (ORCPT ); Sun, 22 Sep 2019 14:50:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:47316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392876AbfIVSuT (ORCPT ); Sun, 22 Sep 2019 14:50:19 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 79740214AF; Sun, 22 Sep 2019 18:50:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569178218; bh=VR7Qr2sSZDvvWUGGowSu7a6WGDqx1uqcGdlqRG8+qwM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WPQpV4ZyMkoe0gDkq3OA66eGwKBJRtEDhtaJfC5zy8iRa85Ffu5AbYiX9D3TeiSWK g63HkV6caYw2gGbblEkPZkwQepSaGJ9vD7qv7O+XnHIi7mvFiH9Czj5zS4ahspdOmg SI6Qs/CEURbYfKnMSRwusQS7d4pUBbOR5e1AQBC4= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Vincent Guittot , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 5.2 022/185] sched/fair: Fix imbalance due to CPU affinity Date: Sun, 22 Sep 2019 14:46:40 -0400 Message-Id: <20190922184924.32534-22-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190922184924.32534-1-sashal@kernel.org> References: <20190922184924.32534-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 b07672e793a81..f72bf8122fe4e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9319,9 +9319,10 @@ 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