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[128.59.11.253]) by mx.google.com with ESMTP id h14-v6si7533894qkh.182.2018.07.25.06.07.21; Wed, 25 Jul 2018 06:07:21 -0700 (PDT) Received-SPF: pass (google.com: domain of kvmarm-bounces@lists.cs.columbia.edu designates 128.59.11.253 as permitted sender) client-ip=128.59.11.253; Authentication-Results: mx.google.com; spf=pass (google.com: domain of kvmarm-bounces@lists.cs.columbia.edu designates 128.59.11.253 as permitted sender) smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 5B4CF4A16C; Wed, 25 Jul 2018 09:07:21 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu X-Spam-Flag: NO X-Spam-Score: -4.201 X-Spam-Level: X-Spam-Status: No, score=-4.201 required=6.1 tests=[BAYES_00=-1.9, DNS_FROM_AHBL_RHSBL=2.699, RCVD_IN_DNSWL_HI=-5] autolearn=unavailable Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 0NEbj-+K2M0p; Wed, 25 Jul 2018 09:07:20 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 309E34A0F7; Wed, 25 Jul 2018 09:07:20 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id BF37B4A0D2 for ; Wed, 25 Jul 2018 09:07:18 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id AIpJtuzAHgbk for ; Wed, 25 Jul 2018 09:07:16 -0400 (EDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 6136140493 for ; Wed, 25 Jul 2018 09:07:16 -0400 (EDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A1EFA80D; Wed, 25 Jul 2018 06:07:15 -0700 (PDT) Received: from [10.4.13.119] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 98C7E3F237; Wed, 25 Jul 2018 06:07:13 -0700 (PDT) Subject: Re: [Qemu-devel] VCPU hotplug on KVM/ARM To: Andrew Jones References: <000e01d3afad$b9a13830$2ce3a890$@codeaurora.org> <20180227104708.GA11391@cbox> <20180227124604.GA2373@cbox> <20180227132131.fipafmnb56a7fj76@kamzik.brq.redhat.com> <74427c65-b860-d576-04f9-766253285210@arm.com> <20180725122806.g2gpvdbrbdkriprg@kamzik.brq.redhat.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: <202a2c63-1a3e-7f01-850c-4fb5e48f43e7@arm.com> Date: Wed, 25 Jul 2018 14:07:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180725122806.g2gpvdbrbdkriprg@kamzik.brq.redhat.com> Content-Language: en-GB Cc: Christoffer Dall , Christoffer Dall , david@redhat.com, qemu-devel@nongnu.org, Christoffer Dall , qemu-arm@nongnu.org, imammedo@redhat.com, kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu X-TUID: ChR+1EqD2zqT On 25/07/18 13:28, Andrew Jones wrote: > On Wed, Jul 25, 2018 at 11:40:54AM +0100, Marc Zyngier wrote: >> On 24/07/18 19:35, Maran Wilson wrote: >>> It's been a few months since this email thread died off. Has anyone >>> started working on a potential solution that would allow VCPU hotplug on >>> KVM/ARM ? Or is this a project that is still waiting for an owner who >>> has the time and inclination to get started? >> >> This is typically a project for someone who would have this particular >> itch to scratch, and who has a demonstrable need for this functionality. >> >> Work wise, it would have to include adding physical CPU hotplug support >> to the arm64 kernel as a precondition, before worrying about doing it in >> KVM. >> >> For KVM itself, particular area of interests would be: >> - Making GICv3 redistributors magically appear in the IPA space >> - Live resizing of GICv3 structures >> - Dynamic allocation of MPIDR, and mapping with vcpu_id > > I have CPU topology description patches on the QEMU list now[*]. A next > step for me is to this MPIDR work. I probably won't get to it until the > end of August though. > > [*] http://lists.nongnu.org/archive/html/qemu-devel/2018-07/msg01168.html > >> >> This should keep someone busy for a good couple of weeks (give or take a >> few months). > > :-) > >> >> That being said, I'd rather see support in QEMU first, creating all the >> vcpu/redistributors upfront, and signalling the hotplug event via the >> virtual firmware. And then post some numbers to show that creating all >> the vcpus upfront is not acceptable. > > I think the upfront allocation, allocating all possible cpus, but only > activating all present cpus, was the planned approach. What were the > concerns about that approach? Just vcpu memory overhead for too many > overly ambitious VM configs? I don't have any ARM-specific concern about that, and I think this is the right approach. It has the good property of not requiring much change in the kernel (other than actually supporting CPU hotplug). vcpu memory overhead is a generic concern though, and not only for ARM. We currently allow up to 512 vcpus per VM, which looks like a lot, but really isn't. If we're to allow this to be bumped up significantly, we should start accounting the vcpu-related memory against the user's allowance... Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm