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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6461C433EF for ; Thu, 14 Oct 2021 15:07:57 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 767D9600CC for ; Thu, 14 Oct 2021 15:07:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 767D9600CC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:51022 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mb2Kq-0001vJ-Gq for qemu-devel@archiver.kernel.org; Thu, 14 Oct 2021 11:07:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40216) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mb2Ho-0008DI-U5 for qemu-devel@nongnu.org; Thu, 14 Oct 2021 11:04:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60988) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mb2Hj-0008Bh-6Z for qemu-devel@nongnu.org; Thu, 14 Oct 2021 11:04:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634223882; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fiaTZGyh8Y8PoVD5FwOqkosYD7LUYaFf78rkttcxqpQ=; b=EZh1jRxwJAvvF/milRSVLsHRVRqqGFGR7ivPX95B6LYlyURmGvfUe1WXyrs4neUm9L3SkH 3V4XUzsIOLdouvlEN9uVZBzqS9rs+ZO4fRAOE6TsYps1DAkgTWGik4v37v5bu4oQbtyr2k FZjrVX5AeIBM2vjEcHUHDqmJtlYgHV0= Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-6-K2EicquONQumglCZusiGoQ-1; Thu, 14 Oct 2021 11:04:40 -0400 X-MC-Unique: K2EicquONQumglCZusiGoQ-1 Received: by mail-qk1-f197.google.com with SMTP id z29-20020a05620a08dd00b0045fa369b83dso4655806qkz.9 for ; Thu, 14 Oct 2021 08:04:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=fiaTZGyh8Y8PoVD5FwOqkosYD7LUYaFf78rkttcxqpQ=; b=DvYdVmthiNFA6wcF0Bvx7UXphe+aHcXUetE4euOfSSCy1Eg9cw45On/D3c3wZEX7D6 y35KeariD2MyRVjOJWZ/LrsbMzzf8KE0FjCE7WCsM2dXexcz3WWPaC9hSOkfo9uIH6D3 w1eKvzoL3+LQda+iboKQhoNZvsHTKGo7jlBcUrDmdmMRWISZ0aSLeWF2OWkNhO0+8nEm g4SeM3J9GVmc30g5rydIlUkPh6BU4qdhpmGC43GQxS1Et7gNuOvM+z8ByMGKjZOOc+Oe aV6R7GFFg3HnC3ye8uFA4+VYwXPPobFLFf3ijW7YZ/fkI3K9ub6nybS71fwGBwlSOJqb Awdw== X-Gm-Message-State: AOAM5335h5SuCbQZEBDqTFTf7zbbjtKl0y+cvCZvWoIvpj6AKjtGx45k yupIVEcn9KWG4MQz9Ox+e8Bi8ERFlmHO2DZyIyvvKxpCc64eVkffFh+NUEzNGm4dsb2+kuQeRDa XooYOihAZsWoChYYDRpNy5kclI1UJHSk= X-Received: by 2002:a37:5446:: with SMTP id i67mr5214454qkb.502.1634223880085; Thu, 14 Oct 2021 08:04:40 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx/JqMZHkmDofskwCeBPxmayMBUVavKj4EOOJ6Mbnpp61SQxPZrlB4HYDBekrShjuF3oEirhfPfVbeC3QS3Qmw= X-Received: by 2002:a37:5446:: with SMTP id i67mr5214428qkb.502.1634223879886; Thu, 14 Oct 2021 08:04:39 -0700 (PDT) MIME-Version: 1.0 References: <20211001070603.307037-1-eperezma@redhat.com> <20211001070603.307037-16-eperezma@redhat.com> <87y26yg6nt.fsf@dusky.pond.sub.org> <87lf2y5p7i.fsf@dusky.pond.sub.org> In-Reply-To: <87lf2y5p7i.fsf@dusky.pond.sub.org> From: Eugenio Perez Martin Date: Thu, 14 Oct 2021 17:04:03 +0200 Message-ID: Subject: Re: [RFC PATCH v4 15/20] vhost: Shadow virtqueue buffers forwarding To: Markus Armbruster Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eperezma@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=eperezma@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Parav Pandit , Juan Quintela , Jason Wang , "Michael S. Tsirkin" , qemu-level , virtualization , Harpreet Singh Anand , Xiao W Wang , Stefan Hajnoczi , Eli Cohen , Eric Blake , Michael Lilja , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 12, 2021 at 3:48 PM Markus Armbruster wrote= : > > Eugenio Perez Martin writes: > > > On Tue, Oct 12, 2021 at 7:21 AM Markus Armbruster w= rote: > >> > >> Eugenio P=C3=A9rez writes: > >> > >> > Initial version of shadow virtqueue that actually forward buffers. T= here > >> > are no iommu support at the moment, and that will be addressed in fu= ture > >> > patches of this series. Since all vhost-vdpa devices uses forced IOM= MU, > >> > this means that SVQ is not usable at this point of the series on any > >> > device. > >> > > >> > For simplicity it only supports modern devices, that expects vring > >> > in little endian, with split ring and no event idx or indirect > >> > descriptors. Support for them will not be added in this series. > >> > > >> > It reuses the VirtQueue code for the device part. The driver part is > >> > based on Linux's virtio_ring driver, but with stripped functionality > >> > and optimizations so it's easier to review. Later commits add simple= r > >> > ones. > >> > > >> > SVQ uses VIRTIO_CONFIG_S_DEVICE_STOPPED to pause the device and > >> > retrieve its status (next available idx the device was going to > >> > consume) race-free. It can later reset the device to replace vring > >> > addresses etc. When SVQ starts qemu can resume consuming the guest's > >> > driver ring from that state, without notice from the latter. > >> > > >> > This status bit VIRTIO_CONFIG_S_DEVICE_STOPPED is currently discusse= d > >> > in VirtIO, and is implemented in qemu VirtIO-net devices in previous > >> > commits. > >> > > >> > Removal of _S_DEVICE_STOPPED bit (in other words, resuming the devic= e) > >> > can be done in the future if an use case arises. At this moment we c= an > >> > just rely on reseting the full device. > >> > > >> > Signed-off-by: Eugenio P=C3=A9rez > >> > --- > >> > qapi/net.json | 2 +- > >> > hw/virtio/vhost-shadow-virtqueue.c | 237 ++++++++++++++++++++++++++= ++- > >> > hw/virtio/vhost-vdpa.c | 109 ++++++++++++- > >> > 3 files changed, 337 insertions(+), 11 deletions(-) > >> > > >> > diff --git a/qapi/net.json b/qapi/net.json > >> > index fe546b0e7c..1f4a55f2c5 100644 > >> > --- a/qapi/net.json > >> > +++ b/qapi/net.json > >> > @@ -86,7 +86,7 @@ > >> > # > >> > # @name: the device name of the VirtIO device > >> > # > >> > -# @enable: true to use the alternate shadow VQ notifications > >> > +# @enable: true to use the alternate shadow VQ buffers fowarding pa= th > >> > >> Uh, why does the flag change meaning half-way through this series? > >> > > > > Before this patch, the SVQ mode just makes an extra hop for > > notifications. Guest ones are now received by qemu via ioeventfd, and > > qemu forwards them to the device using a different eventfd. The > > reverse is also true: the device ones will be received by qemu by > > device call fd, and then qemu will forward them to the guest using a > > different irqfd. > > > > This intermediate step is not very useful by itself, but helps for > > checking that that part of the communication works fine, with no need > > for shadow virtqueue to understand vring format. Doing that way also > > produces smaller patches. > > > > So it makes sense to me to tell what QMP command does exactly at every > > point of the series. However I can directly document it as "use the > > alternate shadow VQ buffers forwarding path" from the beginning. > > > > Does this make sense, or will it be better to write the final > > intention of the command? > > > > Thanks! > > Working your explanation into commit messages and possibly comments > should do. > Got it, I will include them in both. Thanks!