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 lists1p.gnu.org (lists1p.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 905EDC44501 for ; Wed, 15 Jul 2026 15:53:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wk1v2-0000Sa-Ks; Wed, 15 Jul 2026 11:53:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wk1v1-0000SF-52 for qemu-devel@nongnu.org; Wed, 15 Jul 2026 11:53:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wk1uy-0005H8-VQ for qemu-devel@nongnu.org; Wed, 15 Jul 2026 11:53:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784130783; 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:in-reply-to:in-reply-to: references:references; bh=OCLYhPCoaTPzd0cjpjRLz6U09mDfeXipA02PIh9dHWg=; b=JBTmBUsCTJc+0irzdAgdZi4aE2joLRwj7H6hTtt43/O/p5GYew4qYpT8lzpGo840MXX5SV Ao3tjSxdcQF1t7mrO9r4xIdBgLJv0Q5aborSoAjZZyufhjJehCumjb/xApWySZjJvBi8U1 bMl+Z5vCxpc0n14/HVqdVVxtC3vvE3M= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-588-9WyTv9BpNoGS7ij6aBw2cA-1; Wed, 15 Jul 2026 11:53:00 -0400 X-MC-Unique: 9WyTv9BpNoGS7ij6aBw2cA-1 X-Mimecast-MFC-AGG-ID: 9WyTv9BpNoGS7ij6aBw2cA_1784130779 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 38F6818002CC; Wed, 15 Jul 2026 15:52:58 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.221]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 577F230001A4; Wed, 15 Jul 2026 15:52:51 +0000 (UTC) Date: Wed, 15 Jul 2026 16:52:48 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Cc: Michael Tokarev , Vladimir Sementsov-Ogievskiy , jasowang@redhat.com, armbru@redhat.com, peterx@redhat.com, farosas@suse.de, raphael.s.norwitz@gmail.com, bchaney@akamai.com, qemu-devel@nongnu.org, pbonzini@redhat.com, yc-core@yandex-team.ru, mark.caveayland@nutanix.com Subject: Re: [PATCH v19 00/15] virtio-net: live-TAP local migration Message-ID: References: <20260714154246.1242856-1-vsementsov@yandex-team.ru> <20260715114802-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260715114802-mutt-send-email-mst@kernel.org> User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: permerror client-ip=170.10.133.124; envelope-from=berrange@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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=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: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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, Jul 15, 2026 at 11:48:40AM -0400, Michael S. Tsirkin wrote: > On Wed, Jul 15, 2026 at 06:01:39PM +0300, Michael Tokarev wrote: > > On 14.07.2026 18:42, Vladimir Sementsov-Ogievskiy wrote: > > > Hi all! > > > > > > Here is a migration for TAP net backend, including its properties and > > > open fds. > > > > > > With this new feature, management software doesn't need to initialize > > > new TAP and do a switch to it. Nothing should be done around > > > virtio-net in local migration: it just migrates and continues to use > > > same TAP device. So we avoid extra logic in management software, extra > > > allocations in kernel (for new TAP), and corresponding extra delay in > > > migration downtime. > > > > This is quite a big patch set, - is this really worth the effort to do > > all this just for *local* migration? What's the possible use case for > > this in real, - am I right this is just about upgrading the host qemu? > > And with that in mind, isn't it sufficient to use what we already have > > (namely, create new tap, start new qemu instance, and migrate the usual > > way), and tolerate some very minor downtime while the networking code > > learns the new network topology (isn't it happening almost instantly > > anyway, and if not, the management can help by sending gratitious ARP)? > > > > I wonder what's the use for this at yandex? > > > > Thanks, > > > > /mjt > > Well just theoretically, imagine a big VM, reserving twice the amount > of memory just to migrate is not nice at all. Don't we already have the ability to skip memory transfer by setting the "x-ignore-shared" capability, assuming the VM RAM has a shared memory backing. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|