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=-0.8 required=3.0 tests=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 C71E2C4360C for ; Thu, 10 Oct 2019 14:17:55 +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 994DB206B6 for ; Thu, 10 Oct 2019 14:17:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 994DB206B6 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]:40160 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIZGM-0001Cy-Q0 for qemu-devel@archiver.kernel.org; Thu, 10 Oct 2019 10:17:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50243) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIZFb-0000o6-5g for qemu-devel@nongnu.org; Thu, 10 Oct 2019 10:17:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iIZFZ-0004Y4-V8 for qemu-devel@nongnu.org; Thu, 10 Oct 2019 10:17:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49022) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iIZFZ-0004Xv-MF for qemu-devel@nongnu.org; Thu, 10 Oct 2019 10:17:05 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id BAE75307D88C; Thu, 10 Oct 2019 14:17:04 +0000 (UTC) Received: from localhost (ovpn-116-5.gru2.redhat.com [10.97.116.5]) by smtp.corp.redhat.com (Postfix) with ESMTP id 574CB60BE1; Thu, 10 Oct 2019 14:16:54 +0000 (UTC) Date: Thu, 10 Oct 2019 11:16:52 -0300 From: Eduardo Habkost To: Igor Mammedov Subject: Re: [RFC 0/3] acpi: cphp: add CPHP_GET_CPU_ID_CMD command to cpu hotplug MMIO interface Message-ID: <20191010141652.GD21666@habkost.net> References: <20191009132252.17860-1-imammedo@redhat.com> <20191010055356-mutt-send-email-mst@kernel.org> <20191010153815.4f7a3fc9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010153815.4f7a3fc9@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Thu, 10 Oct 2019 14:17:04 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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: "Michael S. Tsirkin" , Laszlo Ersek , qemu-devel@nongnu.org, Gerd Hoffmann , Paolo Bonzini , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Oct 10, 2019 at 03:39:12PM +0200, Igor Mammedov wrote: > On Thu, 10 Oct 2019 05:56:55 -0400 > "Michael S. Tsirkin" wrote: > > > On Wed, Oct 09, 2019 at 09:22:49AM -0400, Igor Mammedov wrote: > > > As an alternative to passing to firmware topology info via new fwcfg files > > > so it could recreate APIC IDs based on it and order CPUs are enumerated, > > > > > > extend CPU hotplug interface to return APIC ID as response to the new command > > > CPHP_GET_CPU_ID_CMD. > > > > One big piece missing here is motivation: > I thought the only willing reader was Laszlo (who is aware of context) > so I skipped on details and confused others :/ > > > Who's going to use this interface? > In current state it's for firmware, since ACPI tables can cheat > by having APIC IDs statically built in. > > If we were creating CPU objects in ACPI dynamically > we would be using this command as well. It would save > us quite a bit space in ACPI blob but it would be a pain > to debug and diagnose problems in ACPI tables, so I'd rather > stay with static CPU descriptions in ACPI tables for the sake > of maintenance. > > > So far CPU hotplug was used by the ACPI, so we didn't > > really commit to a fixed interface too strongly. > > > > Is this a replacement to Laszlo's fw cfg interface? > > If yes is the idea that OVMF going to depend on CPU hotplug directly then? > > It does not depend on it now, does it? > It doesn't, but then it doesn't support cpu hotplug, > OVMF(SMM) needs to cooperate with QEMU "and" ACPI tables to perform > the task and using the same interface/code path between all involved > parties makes the task easier with the least amount of duplicated > interfaces and more robust. > > Re-implementing alternative interface for firmware (fwcfg or what not) > would work as well, but it's only question of time when ACPI and > this new interface disagree on how world works and process falls > apart. > > > If answers to all of the above is yes, then I don't really like it: it > > is better to keep all paravirt stuff in one place, namely in fw cfg. > Lets discuss, what cpu hotplug fwcfg interface could look like in > [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg > mail thread and clarify (dis)likes with concrete reasons. > > So far I managed to convince myself that we ought to reuse > and extend current CPU hotplug interface with firmware features, > to endup with consolidated cpu hotplug process without > introducing duplicate ABIs, but I could be wrong so > lets see if fwcfg will be the better approach. > I was more inclined towards the approach in this patch, because I see it as just a bug fix in the CPU hotplug interface (which should have been using the hardware CPU identifier as the CPU selector since the beginning). Providing the missing information in fw_cfg isn't necessarily bad, but please document it explicitly as a hotplug_cpu_selector => cpu_hardware_id mapping, so people won't use "CPU index" as a generic identifier elsewhere. -- Eduardo