linux-kernel - Re: [RFC PATCH 00/32] ACPI/arm64: add support for virtual cpuhotplug

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Message-ID: <5a5fb237-c28b-d6b5-0425-8f8f0fe1ac79@redhat.com>
Date:   Wed, 13 Sep 2023 08:38:51 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
        loongarch@...ts.linux.dev, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org
Cc:     Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Len Brown <lenb@...nel.org>,
        Rafael Wysocki <rafael@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [RFC PATCH 00/32] ACPI/arm64: add support for virtual cpuhotplug


Hi James,

On 9/13/23 03:01, James Morse wrote:
> On 29/03/2023 03:35, Gavin Shan wrote:
>> On 2/3/23 9:50 PM, James Morse wrote:
> 
>>> If folk want to play along at home, you'll need a copy of Qemu that supports this.
>>> https://github.com/salil-mehta/qemu.git
>>> salil/virt-cpuhp-armv8/rfc-v1-port29092022.psci.present
>>>
>>> You'll need to fix the numbers of KVM_CAP_ARM_HVC_TO_USER and KVM_CAP_ARM_PSCI_TO_USER
>>> to match your host kernel. Replace your '-smp' argument with something like:
>>> | -smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
>>>
>>> then feed the following to the Qemu montior;
>>> | (qemu) device_add driver=host-arm-cpu,core-id=1,id=cpu1
>>> | (qemu) device_del cpu1
>>>
>>>
>>> This series is based on v6.2-rc3, and can be retrieved from:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/ virtual_cpu_hotplug/rfc/v1
> 
>> I give it a try, but the hot-added CPU needs to be put into online
>> state manually. I'm not sure if it's expected or not.
> 
> This is expected. If you want the CPUs to be brought online automatically, you can add
> udev rules to do that.
> 

Yeah, I usually execute the following command to bring the CPU into online state,
after the vCPU is hot added by QMP command.

(qemu) device_add driver=host-arm-cpu,core-id=1,id=cpu1
guest# echo 1 > /sys/devices/system/cpu/cpux/online

James, the series was posted a while ago and do you have plan to respin
and post RFCv2 in near future? :)

Thanks,
Gavin