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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 41E11C4338F for ; Wed, 25 Aug 2021 07:55:12 +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 0147861214 for ; Wed, 25 Aug 2021 07:55:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0147861214 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:58232 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mInkd-0006aE-0w for qemu-devel@archiver.kernel.org; Wed, 25 Aug 2021 03:55:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43936) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mInjw-0005tJ-Us for qemu-devel@nongnu.org; Wed, 25 Aug 2021 03:54:28 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:27960) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mInjv-0003gX-Aj for qemu-devel@nongnu.org; Wed, 25 Aug 2021 03:54:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629878066; 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=NOJNv/Kz4Y/j+VwgbbdbmkcOajUAKszuB3pinQWhbC8=; b=UwD0F9qJIAY8VRLee2BaWWN/x65X0YCubxCL6xS3AvKE7NLGe5dr5eDchU9CRHMhDIc9R1 R/r/SQ78lVk8pDRsOz7L2WIvcJ3JOBt+NpgrGr7iwJmfIiX+tPlOir4su/D+wc3+Ac6AZi AdVnb2Z5mNOAND3ow3d9jXJz/6/ge8A= 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-473-KS6DdbR8NJmY4o8vM-8Mag-1; Wed, 25 Aug 2021 03:54:24 -0400 X-MC-Unique: KS6DdbR8NJmY4o8vM-8Mag-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2CE2C100E422 for ; Wed, 25 Aug 2021 07:54:23 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-4.ams2.redhat.com [10.36.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 40C3B69CB8; Wed, 25 Aug 2021 07:54:14 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id B8E3C11380A9; Wed, 25 Aug 2021 09:54:12 +0200 (CEST) From: Markus Armbruster To: Peter Xu Subject: Re: [PATCH 0/2] dump-guest-memory: Add blocker for migration References: <20210824152721.79747-1-peterx@redhat.com> Date: Wed, 25 Aug 2021 09:54:12 +0200 In-Reply-To: <20210824152721.79747-1-peterx@redhat.com> (Peter Xu's message of "Tue, 24 Aug 2021 11:27:19 -0400") Message-ID: <87zgt66jtn.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.747, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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: Andrew Jones , Juan Quintela , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Leonardo Bras Soares Passos , David Gibson , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Peter Xu writes: > Both dump-guest-memory and live migration have vm state cached internally. > Allowing them to happen together means the vm state can be messed up. Simply > block live migration for dump-guest-memory. > > One trivial thing to mention is we should still allow dump-guest-memory even if > -only-migratable is specified, because that flag should majorly be used to > guarantee not adding devices that will block migration by accident. Dump guest > memory is not like that - it'll only block for the seconds when it's dumping. I recently ran into a similarly unusual use of migration blockers: Subject: -only-migrate and the two different uses of migration blockers (was: spapr_events: Sure we may ignore migrate_add_blocker() failure?) Date: Mon, 19 Jul 2021 13:00:20 +0200 (5 weeks, 1 day, 20 hours ago) Message-ID: <87sg0amuuz.fsf_-_@dusky.pond.sub.org> We appear to use migration blockers in two ways: (1) Prevent migration for an indefinite time, typically due to use of some feature that isn't compatible with migration. (2) Delay migration for a short time. Option -only-migrate is designed for (1). It interferes with (2). Example for (1): device "x-pci-proxy-dev" doesn't support migration. It adds a migration blocker on realize, and deletes it on unrealize. With -only-migrate, device realize fails. Works as designed. Example for (2): spapr_mce_req_event() makes an effort to prevent migration degrate the reporting of FWNMIs. It adds a migration blocker when it receives one, and deletes it when it's done handling it. This is a best effort; if migration is already in progress by the time FWNMI is received, we simply carry on, and that's okay. However, option -only-migrate sabotages the best effort entirely. While this isn't exactly terrible, it may be a weakness in our thinking and our infrastructure. I'm bringing it up so the people in charge are aware :) https://lists.nongnu.org/archive/html/qemu-devel/2021-07/msg04723.html Downthread there, Dave Gilbert opined It almost feels like they need a way to temporarily hold off 'completion' of migratio - i.e. the phase where we stop the CPU and write the device data; mind you you'd also probably want it to stop cold-migrates/snapshots?