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[79.176.10.77]) by smtp.gmail.com with ESMTPSA id 36sm9658196wrp.30.2019.10.10.11.15.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Oct 2019 11:15:47 -0700 (PDT) Date: Thu, 10 Oct 2019 14:15:44 -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: <20191010140934-mutt-send-email-mst@kernel.org> References: <20191009132252.17860-1-imammedo@redhat.com> <20191010055356-mutt-send-email-mst@kernel.org> <20191010153815.4f7a3fc9@redhat.com> <20191010095459-mutt-send-email-mst@kernel.org> <20191010175754.7c62cf8f@Igors-MacBook-Pro> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010175754.7c62cf8f@Igors-MacBook-Pro> 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 05:57:54PM +0200, Igor Mammedov wrote: > > Then we should consider switching acpi to use fw cfg. > > Or build another interface that can scale. > > Could be an option, it would be a pain to write a driver in AML for fwcfg access though > (I've looked at possibility to access fwcfg from AML about a year ago and gave up. > I'm definitely not volunteering for the second attempt and can't even give an estimate > it it's viable approach). > > But what scaling issue you are talking about, exactly? Just this: each new thing we add is an ad-hoc data structure with manually maintained backwards compatibility and no built-in discovery. fw cfg has built-in discovery and we've finally managed to handle compatibility reasonably well. PV is already very problematic. Spreading PV code all over the place like this is a very bad idea. For you CPU hotplug is something that you keep in mind first of all, but someone bringing up a new platform already has a steep hill to climb. Adding tons of custom firmware is not helping things. -- MST