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 1F48FC388F9 for ; Tue, 27 Oct 2020 14:52:03 +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 901622225E for ; Tue, 27 Oct 2020 14:52:02 +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="XrIOo04N" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 901622225E 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]:33766 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kXQKP-0001z8-KZ for qemu-devel@archiver.kernel.org; Tue, 27 Oct 2020 10:52:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43496) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kXPpt-00059P-CI for qemu-devel@nongnu.org; Tue, 27 Oct 2020 10:20:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46354) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kXPpp-0007uq-9R for qemu-devel@nongnu.org; Tue, 27 Oct 2020 10:20:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603808420; 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=+6wzuZdWiWK6SCPBN5ZqOG6K6u8rqMSUCpYSh6r4O40=; b=XrIOo04NNxR0V0jmnRzCNHToXWbNhAQ1AZ56ONyAL9cPwgNZqHHsi5cWf2aLBDoJpGpy6E dq5RelbWsIiAPjvILJp8q0jJkzywAqgxbCOS/XT0FTRkVUsH7UtjANpGM7/QjiQ+OcDAoc lrjgQAQhAVSJjBAtSwdMO3OlISnl5R4= 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-420-r4g3n_rmMKyJf2IqgROXSQ-1; Tue, 27 Oct 2020 10:20:18 -0400 X-MC-Unique: r4g3n_rmMKyJf2IqgROXSQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D2E8C1019629 for ; Tue, 27 Oct 2020 14:20:17 +0000 (UTC) Received: from localhost (unknown [10.40.208.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id D6C755578F; Tue, 27 Oct 2020 14:20:06 +0000 (UTC) Date: Tue, 27 Oct 2020 15:20:04 +0100 From: Igor Mammedov To: Vitaly Kuznetsov Subject: Re: [PATCH RFC] memory: pause all vCPUs for the duration of memory transactions Message-ID: <20201027152004.75aeee2d@redhat.com> In-Reply-To: <87wnzbzspp.fsf@vitty.brq.redhat.com> 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> <219ac264-dcd4-70f0-244f-1bee601aded7@redhat.com> <87wnzbzspp.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=imammedo@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=imammedo@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: -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_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: Eduardo Habkost , David Hildenbrand , qemu-devel@nongnu.org, Peter Xu , "Dr. David Alan Gilbert" , Paolo Bonzini , Laszlo Ersek Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 27 Oct 2020 14:47:14 +0100 Vitaly Kuznetsov wrote: > David Hildenbrand writes: > > >>> 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. > > > > I don't actually know if we have such use-cases but thinking about > e.g. punching a hole in a middle of an existing slot requires: > 1) Resizing the existing slot to its first half > 2) Creating the hole > 3) Creating a new slot for the second half of the slot. > In case we'd like to make this atomic, we need to cover the whole > transaction. But again, I don't know if we have a use-case for it or > not. it usually happens during boot time on x86 where MMIO (re)maps cause punching holes in lower RAM. (you can observe it by tracing MemoryListener::region_add/del hooks) [...]