From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.11]) (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 4F938401494 for ; Tue, 21 Jul 2026 02:33:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784601204; cv=none; b=szejvRvY1EL7rAzSKTkMqoNCep/JS/cyWRMfOWJfw6lVcFatOltw2WJrVeXSVo7gkpNyN1/tDLaNEIiXkyDBiCXYFBNjGzzPbYhmCBjbHDaWDuKJgp9ubohWmJOGZjaDmxzrIN1HHUSmpobfJQsi1olZRIX32O0OIDYqXrKXYwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784601204; c=relaxed/simple; bh=FZHs2jKRxcPPeLOrYIGW71hzJcQhDxvMWag/X5NoLhI=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=SY7FhHKybY8qPr4f0imnx3NTq36Axwz6jLGPoV0cGjr3nAF+kQ7p1HuZIfVVGsVJQXvopFDjk0KDvDq6Y6OrTa6JuNX5lGJXZyPFNUrwd3X9WErQt4qNVQpJ98tlNtpvucsJ5u3z/IEHMApNE1Kgy29pudnVgZO/vjkwmSV9FhM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=NSQe9Ist; arc=none smtp.client-ip=192.198.163.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="NSQe9Ist" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1784601202; x=1816137202; h=from:date:subject:mime-version:content-transfer-encoding: message-id:references:in-reply-to:to:cc; bh=FZHs2jKRxcPPeLOrYIGW71hzJcQhDxvMWag/X5NoLhI=; b=NSQe9IstrBNdt/71B01BJW5LbGezgHFsYlGb9ygCiB3ga9CDh4gdY1H9 x9r1jEmnQ4hgR9aSLm1flCPsAymeh4Q6Mtme38MnV8G9F1daLE/KZcU8i DEhbTglEXtCCmA1J1a4XVdn8XKoxs0CqyfkzoQV4Bg9Mjg44PEXRHp+2B GRSYX54ZGA2to28dHkL/RHj4OMXgfwhdbAIqAoee8F3urDOFt8bbw2oz3 T8wZ7iyb7Z85OMJErwBG3rHdtnulJfFmBkSb4qcGcNLHgm/EW3wzC2xmy pFZzcvNs4w0WZ6BWWfAMSWHr7Xzq5p5boGUUCngXUmEX0UeHzhh9bSwdh g==; X-CSE-ConnectionGUID: LwOLrrpQTuSvGX6MsB4gCA== X-CSE-MsgGUID: O5wT7cLFS6GJmp19Hhl5nw== X-IronPort-AV: E=McAfee;i="6800,10657,11852"; a="95785706" X-IronPort-AV: E=Sophos;i="6.25,175,1779174000"; d="scan'208";a="95785706" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2026 19:33:19 -0700 X-CSE-ConnectionGUID: /2Udcfr+Rq2SjvvRNWKnyA== X-CSE-MsgGUID: ONh8PW/8SYiORhq/YXu4gQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,175,1779174000"; d="scan'208";a="257682265" Received: from unknown (HELO [172.25.112.21]) ([172.25.112.21]) by orviesa007.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2026 19:33:18 -0700 From: Ricardo Neri Date: Mon, 20 Jul 2026 19:43:19 -0700 Subject: [PATCH v6 3/6] sched/fair: Check CPU capacity before comparing group types during load balance Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260720-rneri-fix-cas-clusters-v6-3-bb500bf4afd4@linux.intel.com> References: <20260720-rneri-fix-cas-clusters-v6-0-bb500bf4afd4@linux.intel.com> In-Reply-To: <20260720-rneri-fix-cas-clusters-v6-0-bb500bf4afd4@linux.intel.com> To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Tim C Chen , Chen Yu , Christian Loehle , K Prateek Nayak , Andrea Righi , Barry Song Cc: "Rafael J. Wysocki" , Len Brown , ricardo.neri@intel.com, linux-kernel@vger.kernel.org, Ricardo Neri X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=ed25519-sha256; t=1784601848; l=3276; i=ricardo.neri-calderon@linux.intel.com; s=20250602; h=from:subject:message-id; bh=FZHs2jKRxcPPeLOrYIGW71hzJcQhDxvMWag/X5NoLhI=; b=1OC7BBE+U1rdpCuPw9T0/PPmF0xQz0N/hAbTYvY4IU0h9kVQmpIeVp5BkA+8x9O+bEADC+wrq kZKAlM6JpfYA3jjtof6FxIwo/3FJiovhCZwbRIVk6x0FMOBpsLIt9mD X-Developer-Key: i=ricardo.neri-calderon@linux.intel.com; a=ed25519; pk=NfZw5SyQ2lxVfmNMaMR6KUj3+0OhcwDPyRzFDH9gY2w= update_sd_pick_busiest() may incorrectly select a fully_busy group as the busiest group when its per-CPU capacity exceeds that of the destination CPU. This happens because the type of busiest group is initialized to group_has_spare and allows the fully_busy group to win the type comparison. update_sd_pick_busiest() should not choose a candidate scheduling group with at most one runnable task if its per-CPU capacity is greater than that of the destination CPU. Such a check already exists, but it is done too late: after the type comparison, preventing a subsequent fully_busy group of equal per-CPU capacity from being correctly selected. Move this check to occur before comparing group types. Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") Reviewed-by: Christian Loehle Reviewed-by: Chen Yu Reviewed-by: Tim Chen Reviewed-by: Vincent Guittot Tested-by: Christian Loehle Tested-by: Andrea Righi Signed-off-by: Ricardo Neri --- Changes in v6: * Add Tested-by tag from Andrea. Thanks! Changes in v5: * Added Tested-by tag from Christian. Thanks! Changes in v4: * Dropped note on SMT not being affected since SMT + asym capacity is now supported. * Added Reviewed-by tags from Vincent, Tim, and Chen Yu. Thanks! Changes in v3: * Added a Fixes tag. (Christian) * Added Reviewed-by tag from Christian. Thanks! Changes in v2: * Added a note clarifying that SMT and SD_ASYM_CPUCAPACITY are mutually exclusive. (Tim) * Kept parentheses around bitwise operators for clarity. * Rewrote patch description for clarity. --- kernel/sched/fair.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4e82bc9963e6..9132fcd621dd 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -12056,6 +12056,17 @@ static bool update_sd_pick_busiest(struct lb_env *env, sds->local_stat.group_type != group_has_spare)) return false; + /* + * Candidate sg has no more than one task per CPU and has higher + * per-CPU capacity. Migrating tasks to less capable CPUs may harm + * throughput. Maximize throughput, power/energy consequences are not + * considered. + */ + if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && + (sgs->group_type <= group_fully_busy) && + (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) + return false; + if (sgs->group_type > busiest->group_type) return true; @@ -12162,17 +12173,6 @@ static bool update_sd_pick_busiest(struct lb_env *env, break; } - /* - * Candidate sg has no more than one task per CPU and has higher - * per-CPU capacity. Migrating tasks to less capable CPUs may harm - * throughput. Maximize throughput, power/energy consequences are not - * considered. - */ - if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && - (sgs->group_type <= group_fully_busy) && - (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) - return false; - return true; } -- 2.43.0