From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E74BA3C062F for ; Mon, 8 Jun 2026 13:50:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780926648; cv=none; b=YBjptj44zbiFpKyo9q19Wc8Vo/Ku/zXctjTaMF4xsyQXz+d6VyJilGNLhzGEDExUafQe6RBHkTU90LXCj7FatoAV0UtWIoln/s+hh9R6PXgj0IjgPe2jOLxtLChLQJgcHK9/82Ak02G+pvjpLNGjONISzzmnrtiO4GW60xD8gII= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780926648; c=relaxed/simple; bh=XVXDvXXfjh4qW1B/e3euZQC9LUr6sEG2yqHKxL76NCQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gB5Xd21ScGlhYlbAHI7/ucVXJmwHDdZlQi4cNtaIgT42fmhIvMMcsKp0iKRuA3GymDuz/SrbPc4tWVEONX7kdgjFcptx82YfTF6sHQ3TQMe2tkmhXD+cXpJSNbbW6+jCh+0nkzTL3y2wHJhp323WZJSbcr8NaNButI7dKDhdmMg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=ZA/Uz/hJ; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="ZA/Uz/hJ" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0C5FB244B; Mon, 8 Jun 2026 06:50:39 -0700 (PDT) Received: from [10.1.27.11] (e127648.arm.com [10.1.27.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A83DD3F86F; Mon, 8 Jun 2026 06:50:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1780926643; bh=XVXDvXXfjh4qW1B/e3euZQC9LUr6sEG2yqHKxL76NCQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZA/Uz/hJe+UWepM+rw7ySMX8gj9FJMDojBMQgdNF9jUyZiTTHRCh2yJaOFk58Ed4I +I9HAeiQIBQcNRITeQU387MKJXP6e8gcJAAJsRPOtoxl3eN0p5U7Wm2bJgReEWo5p1 85Bv1ZpJjS7Byb4QYe1kbqYSPo63Z5LWAUMlop5c= Message-ID: Date: Mon, 8 Jun 2026 14:50:38 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/6] sched/fair: Do not skip CPUs of similar capacity with busy SMT siblings To: Ricardo Neri , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Tim C Chen , Chen Yu , Barry Song Cc: "Rafael J. Wysocki" , Andrea Righi , K Prateek Nayak , Len Brown , ricardo.neri@intel.com, linux-kernel@vger.kernel.org References: <20260608-rneri-fix-cas-clusters-v4-0-1526711c944c@linux.intel.com> <20260608-rneri-fix-cas-clusters-v4-1-1526711c944c@linux.intel.com> Content-Language: en-US From: Christian Loehle In-Reply-To: <20260608-rneri-fix-cas-clusters-v4-1-1526711c944c@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/8/26 13:57, Ricardo Neri wrote: > When picking a busiest CPU with only one running task, the function > sched_balance_find_src_rq() skips candidate CPUs if the destination CPU has > less than ~5% extra capacity. This condition only holds if all the SMT > siblings of a CPU are idle. > > SMT siblings share the computing resources of a physical core and this > results in reduced capacity if more than one sibling is busy. > > Skipping a CPU as described would prevent the load balancer from pulling > tasks from a scheduling group previously and correctly identified as > group_smt_balance (i.e., one with more than one task running). > > Do not skip a candidate CPU of similar capacity if it has busy SMT > siblings. > > Signed-off-by: Ricardo Neri Nice find! Reviewed-by: Christian Loehle > [snip]