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 2AA88C433EF for ; Tue, 12 Oct 2021 13:49:54 +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 851C160E9C for ; Tue, 12 Oct 2021 13:49:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 851C160E9C 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]:38136 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1maIAC-0004yx-Ez for qemu-devel@archiver.kernel.org; Tue, 12 Oct 2021 09:49:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48344) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1maI98-0004HN-E2 for qemu-devel@nongnu.org; Tue, 12 Oct 2021 09:48:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42218) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1maI96-0003hL-Pw for qemu-devel@nongnu.org; Tue, 12 Oct 2021 09:48:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634046524; 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=o6Q/hlnT7SUSXbJPb9yIf58DKoWrTsiqekTPcluee7g=; b=GFgG+JsH9SrXXaYn3P7uwR/y8AZx2YHLk9yzSI1kHNY03kIJhXxHKJZMjJFc3bq33tUFnJ fz7LjNnXZTpD7jy2+ruZZWQQBfUqta6DC37NkgZjYlq9gqzo64floGquaoWlrqLF5oAe3a 6plvRGfQNfF9ek/2sNYlj13TjW7KWws= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-357-FHOsvxvPMcePLQrwgWN2QQ-1; Tue, 12 Oct 2021 09:48:43 -0400 X-MC-Unique: FHOsvxvPMcePLQrwgWN2QQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8645C11B4725; Tue, 12 Oct 2021 13:48:41 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-14.ams2.redhat.com [10.36.112.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A25BF2AF99; Tue, 12 Oct 2021 13:48:22 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 0B523113865F; Tue, 12 Oct 2021 15:48:17 +0200 (CEST) From: Markus Armbruster To: Eugenio Perez Martin Subject: Re: [RFC PATCH v4 15/20] vhost: Shadow virtqueue buffers forwarding References: <20211001070603.307037-1-eperezma@redhat.com> <20211001070603.307037-16-eperezma@redhat.com> <87y26yg6nt.fsf@dusky.pond.sub.org> Date: Tue, 12 Oct 2021 15:48:17 +0200 In-Reply-To: (Eugenio Perez Martin's message of "Tue, 12 Oct 2021 15:28:01 +0200") Message-ID: <87lf2y5p7i.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@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=216.205.24.124; envelope-from=armbru@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" , Markus Armbruster , qemu-level , Harpreet Singh Anand , Xiao W Wang , Stefan Hajnoczi , Eli Cohen , virtualization , Eric Blake , Michael Lilja , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eugenio Perez Martin writes: > On Tue, Oct 12, 2021 at 7:21 AM Markus Armbruster wro= te: >> >> Eugenio P=C3=A9rez writes: >> >> > Initial version of shadow virtqueue that actually forward buffers. The= re >> > are no iommu support at the moment, and that will be addressed in futu= re >> > patches of this series. Since all vhost-vdpa devices uses forced IOMMU= , >> > 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 simpler >> > 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 discussed >> > in VirtIO, and is implemented in qemu VirtIO-net devices in previous >> > commits. >> > >> > Removal of _S_DEVICE_STOPPED bit (in other words, resuming the device) >> > can be done in the future if an use case arises. At this moment we can >> > 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 path >> >> 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.