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 BA10F361DB8 for ; Fri, 21 Aug 2026 15:48:11 +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=1787327293; cv=none; b=tncQ+JIH0oP0WlztP73dWsE6oFCxty2v/j+8A9BfGxBabb/7kst5VMYqWIXAimaXTjuSfVdUTdbrAHdMmyarMMP1QKvaLdHC+HNZaBuUfznERbxeuIoheFaBwas3XATC9aFc6P+nlXr+HxfxZBLVeGROHtHDtdMFve4M4gsxVWU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787327293; c=relaxed/simple; bh=CmSvnEyIzit8GPRtexYH2sSMlmY/bbhSyRxLXUOEBUs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nvflresNdERZkZJT12SjEmTTn4stZt0bF9ZwUik5brZPyxIFRLtR07rjhW0up9E2ttP3VFTKnTsjebD3ug7BFf40Tw85IgJc41lOTtKGz4mM2kLWOh2Yp07yvRm6dH96p8exmSHvQDSyzQrwZ3nc9pBE1kI92zwAzmV0hfM8fXQ= 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=Q98VlQGa; 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="Q98VlQGa" Received: from pps.filterd (m0360072.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 67LD1nm21606096; Fri, 21 Aug 2026 15:47:54 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=CmSvnE yIzit8GPRtexYH2sSMlmY/bbhSyRxLXUOEBUs=; b=Q98VlQGar4xhYli1ZjXUjW ASv7aVAhfqGvfgirP3lfudOMKkV53O+mUDaW1ANjL0J1mntYI39Mc1AY7oCgHcVG JDU67+zTGuERcxAoBlMXUJ3vfM+PYClgxsKHZH/74vK/2pESwkDppjoq/WmL5ykT +2mfNYSzROMI06ipOOB3lX3yjJsIi9s9yAtb54M7q5dkteG314MVJ+xJ/4e42Ywq xEnCXMVE2hvo0bEeGy6B0KMVUpIJepR6i2Wn7PRG8RFhzZQuGZVZ/XU415w+H9TK WUjrSqJ2xQ6NzAHTdGfmzfkS3Fz/P+gmkoG1QqjQT7ojL0aJM2SpDpv+0DtgwtFg == 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 4g4yu4j94x-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 21 Aug 2026 15:47:54 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 67LFfMwI024700; Fri, 21 Aug 2026 15:47:53 GMT Received: from smtprelay02.dal12v.mail.ibm.com ([172.16.1.4]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4g32eqnmxs-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 21 Aug 2026 15:47:53 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (smtpav03.dal12v.mail.ibm.com [10.241.53.102]) by smtprelay02.dal12v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 67LFlr3g24380140 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 21 Aug 2026 15:47:53 GMT Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 335CE5805A; Fri, 21 Aug 2026 15:47:53 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 267F25803F; Fri, 21 Aug 2026 15:47:51 +0000 (GMT) Received: from [9.61.26.100] (unknown [9.61.26.100]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Fri, 21 Aug 2026 15:47:50 +0000 (GMT) Message-ID: Date: Fri, 21 Aug 2026 21:17:49 +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 v2] nvme-tcp: pin io_cpu to submitter cpu To: Saravanan D , linux-nvme@lists.infradead.org Cc: kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, axboe@kernel.dk, linux-kernel@vger.kernel.org References: <20260820083634.71689-1-saravanand@crusoe.ai> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260820083634.71689-1-saravanand@crusoe.ai> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=CpuPtH4D c=1 sm=1 tr=0 ts=6a88732a cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=MrSfwY1Xb4bpihXmphsA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: hfjCmmJ383EuCeoag73MAq3rpWbhgPRN X-Proofpoint-GUID: hfjCmmJ383EuCeoag73MAq3rpWbhgPRN X-Proofpoint-Spam-Info: AW1haW4tMjYwODIxMDEyMSBTYWx0ZWRfX5ZrNpEb3dlNj XhWIScb88gBv8Z9/Cx5Qrnkjgmh21eplhKZzxmUGZTUNhAV3U+bmk53GZINdLckDByJTtEp0T5E 2T2r9U3AqA09yfNOg9whviEbWF3InxU= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODIxMDEyMSBTYWx0ZWRfX67ZxSX4yy614 mOfEEIIiY03SJ4yGuNIQ8xJ1sMaC7xY+4zPDsB9eiNQIdkebM22jsE+rjG9UV1v9CjiJt38x8sj WddJ6NVPp0aaxlvsuLCy12HhYMqmZZ17L3Z2sAoJLeRYPwOWoZoWNhvNaVtc/Ie6Qg66+1fcGSj wGr0yfC9dDX0MRQNhh3f0fnQCvPpT5nWA9jqBhCVesRWtIo8MezxYjuH1XbFdZrHPlKKU0BtivC ec8xdmUWugl5+/ZQqSONHJMSxfK8v9V8VHG3O3x9Ey8YiQ3Eds2G82tWKgPeNCg7GLAAnUxNWRt MB0nCPvQqkjV4KP10/h9+G6UYNhnHZmwFDp9F/XL9o5i8EybHWadkE1JJquV4ZP/Y6EDdKQeTlC 7YC0Poa8RDjWd6oC4W/IpaceEvtP78W/6j6KKSR+1MqNr+zQV2Rrq1xOEPnBTKzrG6Va+/pnqIc pVKDiE1b6i2o0VP6WYA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-21_04,2026-08-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 bulkscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 spamscore=0 clxscore=1011 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608210121 On 8/20/26 2:06 PM, Saravanan D wrote: > nvme_tcp_set_queue_io_cpu() picks each queue's io_cpu at connect time, > before any I/O exists, as the least loaded CPU in the queue's blk-mq > map group, and all socket work then runs there for the connection's > lifetime. On hosts that partition CPUs between pinned workloads a map > group can straddle a partition boundary, so the pick can land one > workload's socket processing on CPUs owned by another. On a 384 cpu > multi tenant host with one VM driving ~1.1 GB/s of writes, 9% of > nvme_tcp_io_work executions ran outside the submitting VM's cpuset, > all on io_cpus of boundary straddling map groups, observed by the > neighbor as steal time it did not cause. It seems that here multi tenants shares the same NVMe/TCP controller. Sp if the concern is CPU isolation between tenants, why are multiple tenants sharing the same NVMe/TCP controller? Wouldn't a per-tenant controller/connection provide better isolation and allow each controller's queues to be mapped to the tenant's CPU set? If sharing a controller is required, it would be useful to understand why. Thanks, --Nilay