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[79.176.10.77]) by smtp.gmail.com with ESMTPSA id n125sm2723452qkn.129.2019.10.10.06.59.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Oct 2019 06:59:48 -0700 (PDT) Date: Thu, 10 Oct 2019 09:59:42 -0400 From: "Michael S. Tsirkin" To: Igor Mammedov Subject: Re: [RFC 0/3] acpi: cphp: add CPHP_GET_CPU_ID_CMD command to cpu hotplug MMIO interface Message-ID: <20191010095459-mutt-send-email-mst@kernel.org> 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=iso-8859-1 Content-Disposition: inline In-Reply-To: <20191010153815.4f7a3fc9@redhat.com> Content-Transfer-Encoding: quoted-printable 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: Eduardo Habkost , 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: >=20 > > On Wed, Oct 09, 2019 at 09:22:49AM -0400, Igor Mammedov wrote: > > > As an alternative to passing to firmware topology info via new fwcf= g files > > > so it could recreate APIC IDs based on it and order CPUs are enumer= ated, > > >=20 > > > extend CPU hotplug interface to return APIC ID as response to the n= ew command > > > CPHP_GET_CPU_ID_CMD. =20 > >=20 > > 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 :/ >=20 > > 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. >=20 > If we were creating CPU objects in ACPI dynamically > we would be using this command as well. I'm not sure how it's even possible to create devices dynamically. Well I guess it's possible with LoadTable. Is this what you had in mind? > 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. > >=20 > > 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. >=20 > 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. Then we should consider switching acpi to use fw cfg. Or build another interface that can scale. > > If answers to all of the above is yes, then I don't really like it: i= t > > 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=20 > [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg > mail thread and clarify (dis)likes with concrete reasons. >=20 > 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. >=20 > =20 > > > CC: Laszlo Ersek > > > CC: Eduardo Habkost > > > CC: "Michael S. Tsirkin" > > > CC: Gerd Hoffmann > > > CC: Paolo Bonzini > > > CC: Philippe Mathieu-Daud=E9 > > > CC: Richard Henderson > > > =20 > > > Igor Mammedov (3): > > > acpi: cpuhp: fix 'Command data' description is spec > > > acpi: cpuhp: add typical usecases into spec > > > acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command > > >=20 > > > docs/specs/acpi_cpu_hotplug.txt | 37 +++++++++++++++++++++++++++++= +--- > > > hw/acpi/cpu.c | 15 +++++++++++++ > > > hw/acpi/trace-events | 1 + > > > 3 files changed, 50 insertions(+), 3 deletions(-) > > >=20 > > > --=20 > > > 2.18.1 =20 > >=20