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 3C6B7C05027 for ; Wed, 1 Feb 2023 11:20:29 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pNBA5-000066-IZ; Wed, 01 Feb 2023 06:20:21 -0500 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 1pNBA0-0008Rz-3d for qemu-devel@nongnu.org; Wed, 01 Feb 2023 06:20:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pNB9x-0005lI-7S for qemu-devel@nongnu.org; Wed, 01 Feb 2023 06:20:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675250412; 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=+Rf/ndu1ndlmsrEh9cZrHni1lq7ELUaMh4GsKtwZLQM=; b=Wi/UXRqacuELj9ICKDa33vN72qroX+2iOC2/epHX/V1k/WOPmnLb2/n9oIjcw4Ng1NLm4T D42CC7/RDi8OIJ/ZKpWg644FVwUbuRlDGV3JDCIcNe8nDpNdDM9ucQRVmCzKN6s7vfFRLX MdY0uaRKSHTlZ5guwSP4Nb1j9OY5PCc= Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-657-7rWXKKV2NYWHbGPIvyNyZg-1; Wed, 01 Feb 2023 06:20:09 -0500 X-MC-Unique: 7rWXKKV2NYWHbGPIvyNyZg-1 Received: by mail-ed1-f72.google.com with SMTP id w3-20020a056402268300b00487e0d9b53fso12699739edd.10 for ; Wed, 01 Feb 2023 03:20:09 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=+Rf/ndu1ndlmsrEh9cZrHni1lq7ELUaMh4GsKtwZLQM=; b=LHF8wM3brhiBV0jQT9j+fvW8XsCY5hPO5nKsZGwbvWWDmhoANSh6Zj2sRZgXzN/57X ssymMLQMOi5Q9oEok85T1LkRFISG9QAC5Pa2QD+7S+HlkRA3sEokRb/hBKZjfilKr56P GhVWv8lOF6QwSKZfhOBK4++MMWrpSERhdwMXSOeA3GjcYdSGEDauh6A5a6uUTzsPic7F aDYkGA3y2d8D5LgBLj0pCtoTAVe9jncALz+rb0hAxQfDsiAyIc0k9ZmayHpDLXsYNdt1 1MHHcy2jHcATfJo4K062lCGpW1yzRnUy9s9wGbq709JBXmnp+V4XWjSuxB1JH8WxLj8D 4+OQ== X-Gm-Message-State: AO0yUKXGIML8IA8msF6wVYBrqHoVFWle6JJhY/c9YPADIV8jT6gT8QAp 0T/4zuiq5hl9QOk30SQlKWHs9rTvGpLiLIpB+3AiyxPhzbFH40XwfxpBXkQ/+y6azl0OUtlNwLx UjEMaa1OJn7ph/7o= X-Received: by 2002:a17:906:c13:b0:878:56ae:36e6 with SMTP id s19-20020a1709060c1300b0087856ae36e6mr5723205ejf.35.1675250408180; Wed, 01 Feb 2023 03:20:08 -0800 (PST) X-Google-Smtp-Source: AK7set9i2mMeTRZ8GoVCdqa0HFg5CHi82V7w9+EwekItreT6SujTXCtzlj2ifW5yoqzDsJkskO2vZQ== X-Received: by 2002:a17:906:c13:b0:878:56ae:36e6 with SMTP id s19-20020a1709060c1300b0087856ae36e6mr5723192ejf.35.1675250407939; Wed, 01 Feb 2023 03:20:07 -0800 (PST) Received: from redhat.com ([2.52.144.173]) by smtp.gmail.com with ESMTPSA id cw9-20020a170906c78900b007aece68483csm9966929ejb.193.2023.02.01.03.20.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Feb 2023 03:20:07 -0800 (PST) Date: Wed, 1 Feb 2023 06:20:04 -0500 From: "Michael S. Tsirkin" To: Maxime Coquelin Cc: Eugenio Perez Martin , Jason Wang , Cindy Lu , Stefano Garzarella , qemu-level , Laurent Vivier , Juan Quintela Subject: Re: Emulating device configuration / max_virtqueue_pairs in vhost-vdpa and vhost-user Message-ID: <20230201061709-mutt-send-email-mst@kernel.org> References: <6684066f-452d-a8b3-58b2-b0db2a3c2015@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6684066f-452d-a8b3-58b2-b0db2a3c2015@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 On Wed, Feb 01, 2023 at 12:14:18PM +0100, Maxime Coquelin wrote: > Thanks Eugenio for working on this. > > On 1/31/23 20:10, Eugenio Perez Martin wrote: > > Hi, > > > > The current approach of offering an emulated CVQ to the guest and map > > the commands to vhost-user is not scaling well: > > * Some devices already offer it, so the transformation is redundant. > > * There is no support for commands with variable length (RSS?) > > > > We can solve both of them by offering it through vhost-user the same > > way as vhost-vdpa do. With this approach qemu needs to track the > > commands, for similar reasons as vhost-vdpa: qemu needs to track the > > device status for live migration. vhost-user should use the same SVQ > > code for this, so we avoid duplications. > > > > One of the challenges here is to know what virtqueue to shadow / > > isolate. The vhost-user device may not have the same queues as the > > device frontend: > > * The first depends on the actual vhost-user device, and qemu fetches > > it with VHOST_USER_GET_QUEUE_NUM at the moment. > > * The qemu device frontend's is set by netdev queues= cmdline parameter in qemu > > > > For the device, the CVQ is the last one it offers, but for the guest > > it is the last one offered in config space. > > > > To create a new vhost-user command to decrease that maximum number of > > queues may be an option. But we can do it without adding more > > commands, remapping the CVQ index at virtqueue setup. I think it > > should be doable using (struct vhost_dev).vq_index and maybe a few > > adjustments here and there. > > > > Thoughts? > > I am fine with both proposals. > I think index remapping will require a bit more rework in the DPDK > Vhost-user library, but nothing insurmountable. > > I am currently working on a PoC adding support for VDUSE in the DPDK > Vhost library, and recently added control queue support. We can reuse it > if we want to prototype your proposal. > > Maxime > > > Thanks! > > technically backend knows how many vqs are there, last one is cvq... not sure we need full blown remapping ... -- MST