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Sat, 29 Jun 2024 14:29:46 -0400 X-MC-Unique: rkyJPGPwOluijvoCq5ubtw-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B5F4A19560A2; Sat, 29 Jun 2024 18:29:44 +0000 (UTC) Received: from [10.22.16.40] (unknown [10.22.16.40]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E741419560AA; Sat, 29 Jun 2024 18:29:41 +0000 (UTC) Message-ID: Date: Sat, 29 Jun 2024 14:29:41 -0400 Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: dm-crypt performance regression due to workqueue changes To: Mikulas Patocka , Tejun Heo , Lai Jiangshan Cc: Mike Snitzer , Laurence Oberman , Jonathan Brassow , Ming Lei , Ondrej Kozina , Milan Broz , linux-kernel@vger.kernel.org, dm-devel@lists.linux.dev References: <32fd8274-d5f-3eca-f5d2-1a9117fd8edb@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: <32fd8274-d5f-3eca-f5d2-1a9117fd8edb@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 6/29/24 14:15, Mikulas Patocka wrote: > Hi > > I report that the patch 63c5484e74952f60f5810256bd69814d167b8d22 > ("workqueue: Add multiple affinity scopes and interface to select them") > is causing massive dm-crypt slowdown in virtual machines. > > Steps to reproduce: > * Install a system in a virtual machine with 16 virtual CPUs > * Create a scratch file with "dd if=/dev/zero of=Scratch.img bs=1M > count=2048 oflag=direct" - the file should be on a fast NVMe drive > * Attach the scratch file to the virtual machine as /dev/vdb; cache mode > should be 'none' > * cryptsetup --force-password luksFormat /dev/vdb > * cryptsetup luksOpen /dev/vdb cr > * fio --direct=1 --bsrange=128k-128k --runtime=40 --numjobs=1 > --ioengine=libaio --iodepth=8 --group_reporting=1 > --filename=/dev/mapper/cr --name=job --rw=read > > With 6.5, we get 3600MiB/s; with 6.6 we get 1400MiB/s. > > The reason is that virt-manager by default sets up a topology where we > have 16 sockets, 1 core per socket, 1 thread per core. And that workqueue > patch avoids moving work items across sockets, so it processes all > encryption work only on one virtual CPU. > > The performance degradation may be fixed with "echo 'system' >> /sys/module/workqueue/parameters/default_affinity_scope" - but it is > regression anyway, as many users don't know about this option. > > How should we fix it? There are several options: > 1. revert back to 'numa' affinity > 2. revert to 'numa' affinity only if we are in a virtual machine > 3. hack dm-crypt to set the 'numa' affinity for the affected workqueues > 4. any other solution? Another alternative  is to go back to the old "numa" default if the kernel is running under a hypervisor since the cpu configuration information is likely to be incorrect anyway. The current default of "cache" will remain if not under a hypervisor. Cheers, Longman