From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6C784C4167B for ; Thu, 2 Nov 2023 14:11:54 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qyYPY-0007pG-Sr; Thu, 02 Nov 2023 10:11:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qyYPX-0007oL-Sr for qemu-devel@nongnu.org; Thu, 02 Nov 2023 10:11:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qyYPW-0005si-74 for qemu-devel@nongnu.org; Thu, 02 Nov 2023 10:11:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698934261; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Crl62ADJ0uoEpbVHG3l3MIlFa/mnlR9JP+TsBeqPwfk=; b=D7y3d5Cy7S/B9nMP8y9fi+O8lgDToLqgo3DVIUfT8SWJi3tkv2Oi3xeG+Pi+TxVU8DZTKB HTz/nKD7dGG5sAGtffFvP9EEseTlBh+XnCQstSGNjwkalnrrLAjhigPBUpgyJDe1Xabmw1 Jcrl+3/S8Xlgdu2a87qhSddI+PF2MQ8= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-518-l-ISniKIOJSlCy_ej57rqg-1; Thu, 02 Nov 2023 10:10:55 -0400 X-MC-Unique: l-ISniKIOJSlCy_ej57rqg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8A0181C05193; Thu, 2 Nov 2023 14:10:55 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.34]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E66E02026D4C; Thu, 2 Nov 2023 14:10:53 +0000 (UTC) Date: Thu, 2 Nov 2023 15:10:52 +0100 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Markus Armbruster , Michal Privoznik , Paolo Bonzini , Eduardo Habkost , qemu-block@nongnu.org, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eric Blake , "Michael S. Tsirkin" , Hanna Reitz Subject: Re: [PATCH v2 0/2] virtio-blk: add iothread-vq-mapping parameter Message-ID: References: <20230918161604.1400051-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230918161604.1400051-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.393, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 18.09.2023 um 18:16 hat Stefan Hajnoczi geschrieben: > virtio-blk and virtio-scsi devices need a way to specify the mapping between > IOThreads and virtqueues. At the moment all virtqueues are assigned to a single > IOThread or the main loop. This single thread can be a CPU bottleneck, so it is > necessary to allow finer-grained assignment to spread the load. With this > series applied, "pidstat -t 1" shows that guests with -smp 2 or higher are able > to exploit multiple IOThreads. > > This series introduces command-line syntax for the new iothread-vq-mapping > property is as follows: > > --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothread":"iothread0","vqs":[0,1,2]},...]},...' > > IOThreads are specified by name and virtqueues are specified by 0-based > index. > > It will be common to simply assign virtqueues round-robin across a set > of IOThreads. A convenient syntax that does not require specifying > individual virtqueue indices is available: > > --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothread":"iothread0"},{"iothread":"iothread1"},...]},...' > > There is no way to reassign virtqueues at runtime and I expect that to be a > very rare requirement. > > Note that JSON --device syntax is required for the iothread-vq-mapping > parameter because it's non-scalar. > > Based-on: 20230912231037.826804-1-stefanha@redhat.com ("[PATCH v3 0/5] block-backend: process I/O in the current AioContext") Does this strictly depend on patch 5/5 of that series, or would it just be a missed opportunity for optimisation by unnecessarily running some requests from a different thread? I suspect it does depend on the other virtio-blk series, though: [PATCH 0/4] virtio-blk: prepare for the multi-queue block layer https://patchew.org/QEMU/20230914140101.1065008-1-stefanha@redhat.com/ Is this right? Given that soft freeze is early next week, maybe we should try to merge just the bare minimum of strictly necessary dependencies. Kevin