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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 61B7FC433E0 for ; Wed, 24 Jun 2020 17:57:27 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 32ECA206EB for ; Wed, 24 Jun 2020 17:57:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="agotZ85Q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 32ECA206EB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jo9dx-00072A-RQ; Wed, 24 Jun 2020 17:57:05 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jo9dw-000723-Nz for xen-devel@lists.xenproject.org; Wed, 24 Jun 2020 17:57:04 +0000 X-Inumbo-ID: 1bca9e30-b644-11ea-8117-12813bfff9fa Received: from us-smtp-1.mimecast.com (unknown [207.211.31.81]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id 1bca9e30-b644-11ea-8117-12813bfff9fa; Wed, 24 Jun 2020 17:57:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593021422; 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: in-reply-to:in-reply-to:references:references; bh=PEjyCUyE3sWVZkGYeKg9uWZfDhdSTHNNM4bGtfd+Xg4=; b=agotZ85QLqSCJ/gvIcYNGyJI3gaLcXC1uiZTRNXtgwHsyEvUfE797knzrK6gh4NQfmdXd/ Y/eJYvz60PmimnR75qsd4mt6Qo8JZzoxCTpiKQhkfO46OHIWABjIeixX8wbuJTodJcpQ9P axEpQN55meAbXjqmY+c5bI+bSCEtU2A= 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-63-DH3F2a6MOI6snMh9HIjN3A-1; Wed, 24 Jun 2020 13:56:58 -0400 X-MC-Unique: DH3F2a6MOI6snMh9HIjN3A-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 11116800C64; Wed, 24 Jun 2020 17:56:57 +0000 (UTC) Received: from work-vm (ovpn-112-192.ams2.redhat.com [10.36.112.192]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C03715C557; Wed, 24 Jun 2020 17:56:55 +0000 (UTC) Date: Wed, 24 Jun 2020 18:56:53 +0100 From: "Dr. David Alan Gilbert" To: Jason Andryuk Subject: Re: Migration vmdesc and xen-save-devices-state Message-ID: <20200624175653.GA49433@work-vm> References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.3 (2020-06-14) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel , QEMU , zhang.zhanghailiang@huawei.com Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" * Jason Andryuk (jandryuk@gmail.com) wrote: > Hi, > > At some point, QEMU changed to add a json VM description (vmdesc) > after the migration data. The vmdesc is not needed to restore the > migration data, but qemu_loadvm_state() will read and discard the > vmdesc to clear the stream when should_send_vmdesc() is true. About 5 years ago :-) > xen-save-devices-state generates its migration data without a vmdesc. > xen-load-devices-state in turn calls qemu_loadvm_state() which tries > to load vmdesc since should_send_vmdesc is true for xen. When > restoring from a file, this is fine since it'll return EOF, print > "Expected vmdescription section, but got 0" and end the restore > successfully. > > Linux stubdoms load their migration data over a console, so they don't > hit the EOF and end up waiting. There does seem to be a timeout > though and restore continues after a delay, but we'd like to eliminate > the delay. > > Two options to address this are to either: > 1) set suppress_vmdesc for the Xen machines to bypass the > should_send_vmdesc() check. > or > 2) just send the vmdesc data. > > Since vmdesc is just discarded, maybe #1 should be followed. #1 does sound simple! > If going with #2, qemu_save_device_state() needs to generate the > vmdesc data. Looking at qemu_save_device_state() and > qemu_savevm_state_complete_precopy_non_iterable(), they are both very > similar and could seemingly be merged. qmp_xen_save_devices_state() > could even leverage the bdrv_inactivate_all() call in > qemu_savevm_state_complete_precopy_non_iterable(). > > The would make qemu_save_device_state a little more heavywight, which > could impact COLO. I'm not sure how performance sensitive the COLO > code is, and I haven't measured anything. COLO snapshots are potentially quite sensitive; although we've got a load of other things we could do with speeding up, we could do without making them noticably heavier. Dave > Does anyone have thoughts or opinions on the subject? > > Thanks, > Jason > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK