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 X-Spam-Level: X-Spam-Status: No, score=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 870F9C433E1 for ; Fri, 26 Mar 2021 09:20:08 +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 E70BF61A1A for ; Fri, 26 Mar 2021 09:20:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E70BF61A1A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58326 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lPidS-0004oC-Ms for qemu-devel@archiver.kernel.org; Fri, 26 Mar 2021 05:20:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44202) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lPic7-00044Y-8P for qemu-devel@nongnu.org; Fri, 26 Mar 2021 05:18:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26815) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lPic3-000660-0T for qemu-devel@nongnu.org; Fri, 26 Mar 2021 05:18:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616750318; 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=rtTDmfQbYYqqRZD3Jlsl/SCm40Dyq82G8Vau9UwrWlQ=; b=XDP0E9SqezonhGxxZqwoc9PW3Lc+/4iFVALP6NWgVQQ0LtkaL9eMzRrmixCuKSIrGauGa9 R+STdJr5an5zWUwkrkGAPxc8dVUxId8UYGp5024r4ynN1PmkpQmZU5jYiOVCudHkPyid89 PwtcrRlQSHHdW9EZZjx56bHNZOVoWCc= 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-530-doQmLfb5O-6xcUXvldS50Q-1; Fri, 26 Mar 2021 05:18:34 -0400 X-MC-Unique: doQmLfb5O-6xcUXvldS50Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3CA461009E3E; Fri, 26 Mar 2021 09:18:33 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-10.pek2.redhat.com [10.72.13.10]) by smtp.corp.redhat.com (Postfix) with ESMTP id 09F2C36807; Fri, 26 Mar 2021 09:18:27 +0000 (UTC) Subject: Re: [RFC PATCH v2 0/3] virtio-net: graceful drop of vhost for TAP To: Yuri Benditovich References: <20210322122452.369750-1-yuri.benditovich@daynix.com> From: Jason Wang Message-ID: Date: Fri, 26 Mar 2021 17:18:26 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: Yan Vugenfirer , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , qemu-devel@nongnu.org, "Michael S . Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 在 2021/3/26 下午5:09, Yuri Benditovich 写道: > On Fri, Mar 26, 2021 at 10:51 AM Jason Wang wrote: >> >> 在 2021/3/25 下午5:00, Yuri Benditovich 写道: >>> Hi Jason, >>> >>> This was discussed earlier on the previous series of patches. >>> https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg01829.html >>> There were strong objections from both Daniel and Michael and I feel >>> that the series was rejected. >>> There was Michael's claim: >>> "We did what this patch is trying to change for years now, in >>> particular KVM also seems to happily disable CPU features not supported >>> by kernel so I wonder why we can't keep doing it, with tweaks for some >>> corner cases." >> >> So for cpu feautres, it works since the management have other tool to >> the cpuid. Then management will make sure the migration happens amongs >> the hosts that is compatibile with the same cpuid sets. >> >> For vhost, we don't have such capabilities, that's why I think we need >> to have fallback. >> > Hi Jason, > What, from your POV was the result of v1 discussion? It looks to me we don't have an agreement on that, sorry. > IMO, there was one critical comment that the patch does not address > 'forcevhost' properly (indeed). > IMO, there are many comments from Daniel and Michael that in the sum > say that this change is not what they would like. > If I'm mistaken please let me know. I think I will open a new thread and summarize the different approaches and then we can come a conclusion. > > I have no problem to send v3 = v1 + handling of ''forcevhost' > If this is what you want, please let me know also. > >>> https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg03187.html >>> And it was Michael's question: >>> "Can we limit the change to when a VM is migrated in?" >>> https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg03163.html >>> So I'm trying to suggest another approach: >>> - In case of conflicting features (for example RSS and vhost) we in >>> qemu we do not have enough information to prefer one or another. >>> - If we drop to userspace in the first set_features we say: "vhost is >>> less important than other requested features" >>> - This series keeps backward compatibility, i.e. if you start with >>> vhost and some features are not available - they are silently cleared. >>> - But in case the features are available on source machine - they are used >>> - In case of migration this series says: "We prefer successful >>> migration even if for that we need to drop to userspace" >>> - On the migration back to the 1st system we again work with all the >>> features and with vhost as all the features are available. >> >> One issue for this approach is that. Consider we had two drivers: >> >> 1) Driver A that supports split only >> 2) Driver B that supports packed >> >> Consider src support packed but dest doesn't >> >> So switching driver A to driver B works without migration. But if we >> switch driver from A to B after migration it won't work? > I assume that both src and dest started with vhost=on. > > As driver B supports both packed and split, you can switch from driver > A to driver B after migration > and driver B will work with split. Exactly as it does today. > > The key question is what is more important - vhost or features that > vhost does not support? > current code says: vhost is more important always > v1 patch says: features are more important always. > v2 patch says: vhost is more important at init time, features are more > important at migration time. > Because we are able to drop vhost but we can't drop features when we > have a running driver. > Do you agree? I think what came from cli is the most important. So if I understand correclty: - vhost=on means "turn on vhost when possible" it implies that fallback is allowed (we had already had fallback codes) - vhostforce=on means "turn on vhost unconditonally" it implies that we can't do fallback So my understanding is that: - "vhost=on, packed=on", we can fallback to userspace but must keep packed virtqueue works - "vhost=on,vhostforce=on,packed=on", we can't fallback and must keep both vhost and packed virtqueue work, if we can't we need to fail Thanks > >> Thanks >> >> >>> Thanks, >>> Yuri >>> >>> >>> >>> On Thu, Mar 25, 2021 at 8:59 AM Jason Wang wrote: >>>> 在 2021/3/22 下午8:24, Yuri Benditovich 写道: >>>>> Allow fallback to userspace only upon migration, only for specific features >>>>> and only if 'vhostforce' is not requested. >>>>> >>>>> Changes from v1: >>>>> Patch 1 dropeed (will be submitted in another series) >>>>> Added device callback in case the migration should fail due to missing features >>>> Hi Yuri: >>>> >>>> Have a quick glance at the series. A questions is why we need to do the >>>> fallback only during load? >>>> >>>> I think we should do it in the device initializating. E.g when the vhost >>>> features can not satisfy, we should disable vhost since there. >>>> >>>> Thanks >>>> >>>> >>>>> Yuri Benditovich (3): >>>>> net: add ability to hide (disable) vhost_net >>>>> virtio: introduce 'missing_features_migrated' device callback >>>>> virtio-net: implement missing_features_migrated callback >>>>> >>>>> hw/net/vhost_net.c | 4 ++- >>>>> hw/net/virtio-net.c | 51 ++++++++++++++++++++++++++++++++++++++ >>>>> hw/virtio/virtio.c | 8 ++++++ >>>>> include/hw/virtio/virtio.h | 8 ++++++ >>>>> include/net/net.h | 1 + >>>>> 5 files changed, 71 insertions(+), 1 deletion(-) >>>>>