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 D31FAC07545 for ; Wed, 25 Oct 2023 15:25:51 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qvflI-0001vt-TO; Wed, 25 Oct 2023 11:25:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qvflH-0001vb-M9 for qemu-devel@nongnu.org; Wed, 25 Oct 2023 11:25:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qvflG-0005fC-1q for qemu-devel@nongnu.org; Wed, 25 Oct 2023 11:25:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698247533; 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=ELvQYxtueYWS5mp8ZKcJro7XbxrWmhJTuQySz+q+dWI=; b=fD2YjM75ZgPowWLyZve69LwVZwNqpo/OCuBF+CwVFKviPwtdjQUd1LMDSlNyh4M35vyQWs pIf42UTdNcGdwbMaYTHxB+S5PZtDwUB1Ppf8G1QqivnM401fIOj4edfl82OqoV3AgL5N72 Z/S2LAjCIHjGh+M0YZmuI7BZDq1MAj8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-441-3Wm45M9ROrqykCJMIiecZQ-1; Wed, 25 Oct 2023 11:25:28 -0400 X-MC-Unique: 3Wm45M9ROrqykCJMIiecZQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0C7158870E1; Wed, 25 Oct 2023 15:25:27 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.154]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D403C1C060AE; Wed, 25 Oct 2023 15:25:25 +0000 (UTC) Date: Wed, 25 Oct 2023 16:25:23 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: Fabiano Rosas , qemu-devel@nongnu.org, armbru@redhat.com, Juan Quintela , Leonardo Bras , Claudio Fontana , Eric Blake Subject: Re: [PATCH v2 06/29] migration: Add auto-pause capability Message-ID: References: <20231023203608.26370-1-farosas@suse.de> <20231023203608.26370-7-farosas@suse.de> <87y1fqerev.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; 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_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: 2.1.29 Precedence: list List-Id: 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, Oct 25, 2023 at 10:58:16AM -0400, Peter Xu wrote: > On Wed, Oct 25, 2023 at 03:20:16PM +0100, Daniel P. Berrangé wrote: > > On Wed, Oct 25, 2023 at 10:57:12AM -0300, Fabiano Rosas wrote: > > > Daniel P. Berrangé writes: > > > > > > > On Mon, Oct 23, 2023 at 05:35:45PM -0300, Fabiano Rosas wrote: > > > >> Add a capability that allows the management layer to delegate to QEMU > > > >> the decision of whether to pause a VM and perform a non-live > > > >> migration. Depending on the type of migration being performed, this > > > >> could bring performance benefits. > > > > > > > > I'm not really see what problem this is solving. > > > > > > > > > > Well, this is the fruit of your discussion with Peter Xu in the previous > > > version of the patch. > > > > > > To recap: he thinks QEMU is doing useless work with file migrations > > > because they are always asynchronous. He thinks we should always pause > > > before doing fixed-ram migration. You said that libvirt would rather use > > > fixed-ram for a more broad set of savevm-style commands, so you'd rather > > > not always pause. I'm trying to cater to both of your wishes. This new > > > capability is the middle ground I came up with. > > > > > > So fixed-ram would always pause the VM, because that is the primary > > > use-case, but libvirt would be allowed to say: don't pause this time. > > > > If the VM is going to be powered off immediately after saving > > a snapshot then yes, you might as well pause it, but we can't > > assume that will be the case. An equally common use case > > would be for saving periodic snapshots of a running VM. This > > should be transparent such that the VM remains running the > > whole time, except a narrow window at completion of RAM/state > > saving where we flip the disk snapshots, so they are in sync > > with the RAM snapshot. > > Libvirt will still use fixed-ram for live snapshot purpose, especially for > Windows? Then auto-pause may still be useful to identify that from what > Fabiano wants to achieve here (which is in reality, non-live)? > > IIRC of previous discussion that was the major point that libvirt can still > leverage fixed-ram for a live case - since Windows lacks efficient live > snapshot (background-snapshot feature). Libvirt will use fixed-ram for all APIs it has that involve saving to disk, with CPUs both running and paused. > From that POV it sounds like auto-pause is a good knob for that. >From libvirt's POV auto-pause will create extra work for integration for no gain. 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 :|