From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 280DC1E505 for ; Wed, 26 Mar 2025 12:57:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742993873; cv=none; b=hFLimu3MD83g/t1MfcHvLGtBLTqxGcX5te+QEsbHX2boUOvwt2h+0rya6lIQvAMQhTHZzwtXI6BASA34ikzhQ8gd3GcGiCN88W97t6TipXvxqA0ICdcFwfRhkl2USGU5hJJ1NkFvKGTBTHWTPfkAprmoVdZb+PJB1LlpNCHj06w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742993873; c=relaxed/simple; bh=fMfWkXzrzG6b2b7FJDG+sP3cB3Nluk75FDYwaksyX+0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rLyjFOHKKJLSC2OQs6oSsiiaCG60L0SiwSllFAwi8RDCLoUul0mCc7y4bFznpXQS8ip/fSIWjZrqxstqO+07OcuBX3eBYqBoyBS7RzhUhrCW6s/95lCSC96fzMOaOqYJfManvUts7r8fgXazCVqma72INs6cVg6G4HkSqbau2SI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=TySHglpC; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="TySHglpC" Received: from pps.filterd (m0360072.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 52Q2aajM027823; Wed, 26 Mar 2025 12:57:37 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=fUL5kU Pao1qlI7NeuB9QYIUz5zCNvVxpyyXsrRJII9Y=; b=TySHglpCKSBIrbNycBRkN4 km/yaMOZC3MMbPWk/XTrelgWH8JGyYuGuzDjh55XgwilEThBoM4fzaSr0RMQxNxz GWC8Xv4V4bh2DIR40qQU3/i3Rh5O8KJwIvtL1+LVUwdKP3BbobLx+64jtS6oeLnd hGRBmljCs1FI2bwKCn8wTf6W3BaVLnEcJYPdYHa1klX7fR4kHtHdYaTCtli4Lvpy BxzRr3JilXj4PbMOCyQAvlmDFNA14PUS3nxRlFUL4F1bhmRl3Y8PvX+60CSo7mDM RkbaDmqeYvcqs0QXznJuX8eQkEKJX8dXgVLzrw6eKs2Qtgtb5p9lccvQ0+HloI2g == Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 45kbjx2wrm-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 26 Mar 2025 12:57:37 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 52Q9QV96030321; Wed, 26 Mar 2025 12:57:25 GMT Received: from smtprelay03.fra02v.mail.ibm.com ([9.218.2.224]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 45j7htgk5n-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 26 Mar 2025 12:57:25 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 52QCvNSc42533140 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 26 Mar 2025 12:57:23 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 632FB20043; Wed, 26 Mar 2025 12:57:23 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 114AF20040; Wed, 26 Mar 2025 12:57:21 +0000 (GMT) Received: from [9.124.217.36] (unknown [9.124.217.36]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 26 Mar 2025 12:57:20 +0000 (GMT) Message-ID: <4d0059f1-d834-44d5-bc57-7425980f5a97@linux.ibm.com> Date: Wed, 26 Mar 2025 18:27:20 +0530 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 v10 20/21] futex: Implement FUTEX2_NUMA To: Peter Zijlstra , Sebastian Andrzej Siewior Cc: =?UTF-8?Q?Andr=C3=A9_Almeida?= , Darren Hart , Davidlohr Bueso , Ingo Molnar , Juri Lelli , Thomas Gleixner , Valentin Schneider , Waiman Long , linux-kernel@vger.kernel.org References: <20250312151634.2183278-1-bigeasy@linutronix.de> <20250312151634.2183278-21-bigeasy@linutronix.de> <20250325225600.GP36322@noisy.programming.kicks-ass.net> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20250325225600.GP36322@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: i7wHBrpXkj4opd2FgNFTB970h7W7bhkx X-Proofpoint-ORIG-GUID: i7wHBrpXkj4opd2FgNFTB970h7W7bhkx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-26_06,2025-03-26_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 spamscore=0 clxscore=1015 bulkscore=0 adultscore=0 suspectscore=0 malwarescore=0 mlxlogscore=524 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2503260079 On 3/26/25 04:26, Peter Zijlstra wrote: > On Wed, Mar 26, 2025 at 01:22:19AM +0530, Shrikanth Hegde wrote: > >>> + return &futex_queues[node][hash & futex_hashmask]; > > ^^^^^^^ > >>> + hashsize = 256 * num_possible_cpus(); >>> + hashsize /= num_possible_nodes(); >> >> Wouldn't it be better to use num_online_nodes? each node may get a bigger >> hash bucket which means less collision no? > > No. There are two problems with num_online_nodes, and both are evident > above. > > Consider the case of a sparse set. I am sorry, i didn't understand. Could you please explain?