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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]:58830 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kXPCb-0008Th-Dt for qemu-devel@archiver.kernel.org; Tue, 27 Oct 2020 09:39:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57746) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kXP88-0002ZQ-IR for qemu-devel@nongnu.org; Tue, 27 Oct 2020 09:35:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:52955) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kXP85-0000w6-KR for qemu-devel@nongnu.org; Tue, 27 Oct 2020 09:35:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603805712; 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=5kt11jFdffqZX72kckWEauMzWDnxMg8qtaeRoY4kAMk=; b=fQOVEl7f3Y5cA8zqfDgB8uFIp5s9GD0wfj8mQRncUHW2IqeyQCRAqqyNpi8VIrfddfLlUl RLfmXCGXd9Uki4Tpnck09cohE5c2uHbQkTbF9j1eP2kwzxr3dK4HNKOE/PzrNUrzpYHU9v FXj4OMZrrw1IcdiUo8whRihmRBRLnqw= 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-262-DguBrrtnM6OeyyiBBs4LzA-1; Tue, 27 Oct 2020 09:35:10 -0400 X-MC-Unique: DguBrrtnM6OeyyiBBs4LzA-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 9A387809DD5 for ; Tue, 27 Oct 2020 13:35:09 +0000 (UTC) Received: from [10.36.113.185] (ovpn-113-185.ams2.redhat.com [10.36.113.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1BB5460C07; Tue, 27 Oct 2020 13:35:04 +0000 (UTC) Subject: Re: [PATCH RFC] memory: pause all vCPUs for the duration of memory transactions To: Vitaly Kuznetsov , qemu-devel@nongnu.org References: <20201026084916.3103221-1-vkuznets@redhat.com> <294a987d-b0ef-1b58-98ac-0d4d43075d6e@redhat.com> <87imav26d8.fsf@vitty.brq.redhat.com> <87a6w72565.fsf@vitty.brq.redhat.com> <875z6v24e2.fsf@vitty.brq.redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <219ac264-dcd4-70f0-244f-1bee601aded7@redhat.com> Date: Tue, 27 Oct 2020 14:35:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <875z6v24e2.fsf@vitty.brq.redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/27 01:06:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 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, NICE_REPLY_A=-2.167, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Laszlo Ersek , Eduardo Habkost , Peter Xu , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" >> Same applies to all other kinds of operations (splitting, punching out, >> ...) as you also mentioned. > > One question from a QEMU newbie though: why do you put > kvm_ioctl_inhibit_begin()/kvm_ioctl_inhibit_end() to kvm_region_resize() > only and not taking it all the way up to > memory_region_transaction_begin()/memory_region_transaction_end() to > support atomicity for all kinds of updates right away? The clean way to implement it for memory_region_transaction_begin()/memory_region_transaction_end() is by implementing ->begin() ->commit() callbacks for the KVM MemoryListener, and doing it in there, in KVM code. Now, I wasn't sure how this might affect real-time workloads, where you really don't want to kick CPUs out of KVM. You can make a lot of operations without requiring this handling like 1. Adding regions (memory hotplug) 2. Removing regions (memory hotunplug) 3. Enabling/disabling dirty logging Resize/split(/move/...) are the problematic operations where we would need that handling. Modifying the size/location of existing slots. One way to tackle it would be to "sense" upfront if such "modifying" operations will be required, communicating that via "->begin()", and letting the KVM notifier decide based on that information whether to get everything out of KVM. Sounds feasible. > > The second question is whether you plan to sumbit this any time soon) Once we have an agreement on how to proceed, either I can try to dedicate some time, or if you have some time, you can pickup my work and make it also handle the other problematic cases (as discussed e.g., ^). -- Thanks, David / dhildenb