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=-2.0 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 610A5CA90AF for ; Wed, 13 May 2020 14:20:08 +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 0BBD5204EA for ; Wed, 13 May 2020 14:20:08 +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="ig97InbE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BBD5204EA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58478 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jYsEx-00049v-8c for qemu-devel@archiver.kernel.org; Wed, 13 May 2020 10:20:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53894) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jYsDB-0000qO-Rz for qemu-devel@nongnu.org; Wed, 13 May 2020 10:18:17 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:55085 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jYsDB-0006wj-2x for qemu-devel@nongnu.org; Wed, 13 May 2020 10:18:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589379496; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gXGdSORgwy0YhV9ke/TpJnkGKmr4elIO9TcGH0MaN7M=; b=ig97InbEE84S9f38oPi9L0HU3szmhPyYSiBTZQ3RYjkLXcpnm/0kD+nqxzYo3AgNl3GWmj Nu0VdG81GS2lV2ui0SoCRe/Dnas3JEvF2OWO09fADV4S9oEmXWtza3NpbUyPlsxNXTb50T mWC6/CK/OrVIG7I65KI+ZujBoitKajE= 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-459-XdHzdVXdP5CQoY9a-lV-Kg-1; Wed, 13 May 2020 10:18:12 -0400 X-MC-Unique: XdHzdVXdP5CQoY9a-lV-Kg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 69FFF18FF66C; Wed, 13 May 2020 14:18:11 +0000 (UTC) Received: from [10.3.116.145] (ovpn-116-145.phx2.redhat.com [10.3.116.145]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 62EEF619B1; Wed, 13 May 2020 14:18:05 +0000 (UTC) Subject: Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu To: Kevin Wolf , "Dr. David Alan Gilbert" References: <20200511121714.GL1135885@redhat.com> <20200511154645.GI2811@work-vm> <20200512113206.62836e44@luklap> <20200512094337.GK1191162@redhat.com> <20200513103245.GD6202@linux.fritz.box> <20200513105359.GF3225@work-vm> <20200513111320.GE6202@linux.fritz.box> <20200513125624.GJ3225@work-vm> <20200513130849.GD1253949@redhat.com> <20200513134856.GK3225@work-vm> <20200513140650.GH6202@linux.fritz.box> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Wed, 13 May 2020 09:18:05 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200513140650.GH6202@linux.fritz.box> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/13 04:17:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: Lukas Straub , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , qemu-block , Juan Quintela , qemu-devel , Max Reitz , Paolo Bonzini , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/13/20 9:06 AM, Kevin Wolf wrote: >>>>> One more thing to consider is, what if a single object has multiple >>>>> connections? In the case of node-names, we have a limited set of allowed >>>>> characters, so we can use one of the remaining characters as a separator >>>>> and then suffix a counter. In other places, the identifier isn't >>>>> restricted, so suffixing doesn't work. Maybe prefixing does, but it >>>>> would have to be there from the beginning then. >>>> >>>> Yeh I worry about whether on nbd if you can have multiple nbd >>>> connections to one block device. >>> >>> The kernel NBD driver now supports multiple parallel connections. >>> QEMU hasn't implemented this in its NBD code yet, but I certainly >>> see that being in scope for future. >> >> It's not parallel for performance that worries me, it's more about >> separateq connections for separate uses - e.g. if we're serving the same >> read-only disk to multiple separate things. > > That would be a concern for the NBD server. I'm not sure if anything in > QEMU ever waits for NBD servers (except for the client on the other side > of the connection, of course), so there might be no use case for yanking > their connections. > > Anyway, here we were talking about the NBD client, which always accesses > one disk. If you access a second disk, you have a second NBD block node. Ah, right, that's the other direction. No, we do not currently support a single qemu block node backed by multiple NBD clients to one (or more, if they are serving identical content in a failover scenario) NBD servers. Performance could indeed be potentially improved by doing that, but for now, every time qemu behaves as a new NBD client, it is via an additional block node. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org