From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A4DAA495C2; Thu, 30 Nov 2023 16:24:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="vHYrVvcj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33700C433C8; Thu, 30 Nov 2023 16:24:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1701361445; bh=zrw24OEakGJPrVYJ6C58IcSlYLLE+G+SagM2UEEYyUU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vHYrVvcjzJJ+zojwkjqcAw3Jtytn00anIM9VHGFdZq2sRZTajRhv8XRZLZIkPLiWv a+o8vfCxxW0C3Ni5NFVpvT9Ai1P4wCnfjxjtU1JEjzYFlg7w5J2Y/Niewxf7AYIAOG KzRgfKeJoEjzwVf9H8ABCXOCaQOG2Cwks3SSBluI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Keisuke Nishimura , "Peter Zijlstra (Intel)" , Chen Yu , Shrikanth Hegde , Vincent Guittot , Sasha Levin Subject: [PATCH 6.6 006/112] sched/fair: Fix the decision for load balance Date: Thu, 30 Nov 2023 16:20:53 +0000 Message-ID: <20231130162140.520284934@linuxfoundation.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231130162140.298098091@linuxfoundation.org> References: <20231130162140.298098091@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Keisuke Nishimura [ Upstream commit 6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3 ] should_we_balance is called for the decision to do load-balancing. When sched ticks invoke this function, only one CPU should return true. However, in the current code, two CPUs can return true. The following situation, where b means busy and i means idle, is an example, because CPU 0 and CPU 2 return true. [0, 1] [2, 3] b b i b This fix checks if there exists an idle CPU with busy sibling(s) after looking for a CPU on an idle core. If some idle CPUs with busy siblings are found, just the first one should do load-balancing. Fixes: b1bfeab9b002 ("sched/fair: Consider the idle state of the whole core for load balance") Signed-off-by: Keisuke Nishimura Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Chen Yu Reviewed-by: Shrikanth Hegde Reviewed-by: Vincent Guittot Link: https://lkml.kernel.org/r/20231031133821.1570861-1-keisuke.nishimura@inria.fr Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0351320148177..fa9fff0f9620d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11121,12 +11121,16 @@ static int should_we_balance(struct lb_env *env) continue; } - /* Are we the first idle CPU? */ + /* + * Are we the first idle core in a non-SMT domain or higher, + * or the first idle CPU in a SMT domain? + */ return cpu == env->dst_cpu; } - if (idle_smt == env->dst_cpu) - return true; + /* Are we the first idle CPU with busy siblings? */ + if (idle_smt != -1) + return idle_smt == env->dst_cpu; /* Are we the first CPU of this group ? */ return group_balance_cpu(sg) == env->dst_cpu; -- 2.42.0