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 16469C433EF for ; Wed, 16 Mar 2022 11:04:20 +0000 (UTC) Received: from localhost ([::1]:55758 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nURRy-0000zY-N5 for qemu-devel@archiver.kernel.org; Wed, 16 Mar 2022 07:04:18 -0400 Received: from eggs.gnu.org ([209.51.188.92]:58478) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUROw-0007e4-Vp for qemu-devel@nongnu.org; Wed, 16 Mar 2022 07:01:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:34197) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUROs-0001ce-QI for qemu-devel@nongnu.org; Wed, 16 Mar 2022 07:01:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647428464; h=from:from:reply-to: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=rbTD7irnr98vBnl71fHv1aE+5fSIv54WEwV6X1cv87I=; b=V6WQFMW/RiG3MXiFf8iI43gFA5lIeZ9L002WXFDQ2cOjnSrIUhkriLQZUG+bXf7SXCN1Hj THPwg39TVO/a/v6voVf9iTEsiD6rD9YGz/Qn1EY6S53s0fbHt+ulKADqsGN2EExdnhcd6w jXOSdFyBUv/viT212V+ORATlF/pEUKE= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-8-Sv7HmbVgMcaIzQoFWPC4Mw-1; Wed, 16 Mar 2022 07:00:58 -0400 X-MC-Unique: Sv7HmbVgMcaIzQoFWPC4Mw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3910A3804060 for ; Wed, 16 Mar 2022 11:00:58 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B0C1A141DEDB; Wed, 16 Mar 2022 11:00:56 +0000 (UTC) Date: Wed, 16 Mar 2022 11:00:53 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Subject: Re: Time to introduce a migration protocol negotiation (Re: [PATCH v2 00/25] migration: Postcopy Preemption) Message-ID: References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, 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_H5=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Paolo Bonzini , Juan Quintela , "Dr. David Alan Gilbert" , Leonardo Bras Soares Passos , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Mar 16, 2022 at 06:40:08PM +0800, Peter Xu wrote: > On Wed, Mar 16, 2022 at 09:59:28AM +0000, Daniel P. Berrangé wrote: > > On Wed, Mar 16, 2022 at 11:30:59AM +0800, Peter Xu wrote: > > > On Tue, Mar 15, 2022 at 11:15:41AM +0000, Daniel P. Berrangé wrote: > > > > > I still remember you mentioned the upper layer softwares can have > > > > > assumption on using only 1 pair of socket for migration, I think that makes > > > > > postcopy-preempt by default impossible. > > > > > > > > > > Why multifd is different here? > > > > > > > > It isn't different. We went through the pain to extending libvirt > > > > to know how to open many channels for multifd. We'll have todo > > > > the same with this postcopy-pre-empt. To this day though, management > > > > apps above libvirt largely don't enable multifd, which is a real > > > > shame. This is the key reason I think we need to handle this at > > > > the QEMU level automatically. > > > > > > But I still don't undertand how QEMU could know about those tunnels, which > > > should be beyond QEMU's awareness? > > > > > > The tunneling program can be some admin initiated socat tcp forwarding > > > programs, which by default may not allow >1 socket pairs. > > > > > > Or maybe I have mis-understood on what's the tunneling we're discussing? > > > > I dont think I was talking about tunneling at all, just QEMU > > migration protocol options ! > > Ah. :) > > > > > If an app is tunnelling QEMU's migration protocol over some > > channel, that isn't important to QEMU - regardless whether a > > passed in 'fd:' protocol FD is a direct TCP socket, or a > > UNIX socket for a tunnel, QEMU works the same way. In one > > of my other replies I mention a way to make 'fd:' work with > > an arbitrary number of channels, by using an event from QEMU > > to request the app provide additional FDs. > > I very much agree on the whole concept of what you proposed, either on the > new negotiation phase itself, or the idea that with the negotiation phase > we can try to auto-enable some features we not used to. > > What I wanted to express is we can't enable either preempt mode or multifd > automatically from qemu even with them, because these two are quite special > IMHO in that qemu doesn't know whether the mgmt app can handle the multiple > socket pairs. Yes we could teach qemu to dynamically accept new "fd"s, but > again IMHO that still needs to be intervened by the mgmt app. My proposal absolutely *can* let QEMU do that automatically, and that is one of the most important benefits of it. [quote] Introduce one *final-no-more-never-again-after-this* migration capability called "protocol-negotiation". When that capability is set, first declare that henceforth the migration transport is REQUIRED to support **multiple**, **bi-directional** channels. We might only use 1 TCP channel in some cases, but it declares our intent that we expect to be able to use as many channels as we see fit henceforth. [/quote] IOW, any management app that enabled 'protocol-negotiation' is explicitly declaring that it accepts the new requirements for support for multiple channels. An app which enabled 'protocol-negotiation' capability while only allowing 1 chanels is simply broken, because it would be violating the documented requirements for the capability. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|