linux-kernel - RE: [RFC PATCH v3 4/9] hw/arm/virt: Initialize the present cpu members

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Date:   Tue, 18 May 2021 07:04:51 +0000
From:   Salil Mehta <salil.mehta@...wei.com>
To:     "wangyanan (Y)" <wangyanan55@...wei.com>
CC:     Peter Maydell <peter.maydell@...aro.org>,
        Andrew Jones <drjones@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Shannon Zhao <shannon.zhaosl@...il.com>,
        "Alistair Francis" <alistair.francis@....com>,
        David Gibson <david@...son.dropbear.id.au>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "qemu-arm@...gnu.org" <qemu-arm@...gnu.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Philippe Mathieu-Daudé <philmd@...hat.com>,
        yangyicong <yangyicong@...wei.com>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        "Wanghaibin (D)" <wanghaibin.wang@...wei.com>,
        zhukeqian <zhukeqian1@...wei.com>,
        yuzenghui <yuzenghui@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxarm@...neuler.org" <linuxarm@...neuler.org>
Subject: RE: [RFC PATCH v3 4/9] hw/arm/virt: Initialize the present cpu
 members

> From: wangyanan (Y)
> Sent: Tuesday, May 18, 2021 5:43 AM
> 
> Hi Salil,
> 
> On 2021/5/18 4:48, Salil Mehta wrote:
> >> From: Qemu-arm
> [mailto:qemu-arm-bounces+salil.mehta=huawei.com@...gnu.org]
> >> On Behalf Of Yanan Wang
> >> Sent: Sunday, May 16, 2021 11:29 AM
> >> To: Peter Maydell <peter.maydell@...aro.org>; Andrew Jones
> >> <drjones@...hat.com>; Michael S . Tsirkin <mst@...hat.com>; Igor Mammedov
> >> <imammedo@...hat.com>; Shannon Zhao <shannon.zhaosl@...il.com>; Alistair
> >> Francis <alistair.francis@....com>; David Gibson
> >> <david@...son.dropbear.id.au>; qemu-devel@...gnu.org; qemu-arm@...gnu.org
> >> Cc: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>; zhukeqian
> >> <zhukeqian1@...wei.com>; yangyicong <yangyicong@...wei.com>; Zengtao (B)
> >> <prime.zeng@...ilicon.com>; Wanghaibin (D) <wanghaibin.wang@...wei.com>;
> >> yuzenghui <yuzenghui@...wei.com>; Paolo Bonzini <pbonzini@...hat.com>;
> >> Philippe Mathieu-Daudé <philmd@...hat.com>
> >> Subject: [RFC PATCH v3 4/9] hw/arm/virt: Initialize the present cpu members
> >>
> >> We create and initialize a cpuobj for each present cpu in
> >> machvirt_init(). Now we also initialize the cpu member of
> >> structure CPUArchId for each present cpu in the function.
> > [...]
> >
> >>           qdev_realize(DEVICE(cpuobj), NULL, &error_fatal);
> >> +
> >> +        /*
> >> +         * As ARM cpu hotplug is not supported yet, we initialize
> >> +         * the present cpu members here.
> >> +         */
> >> +        machine->possible_cpus->cpus[n].cpu = cpuobj;
> >
> > when vcpu Hotplug is not supported yet, what necessitates this change now?
> >
> The initialization will gives a way to determine whether a CPU is
> present or not.
> At least, for now it will be used when generating ACPI tables, e.g.
> DSDT, MADT.
> See patch 5 and 6.

yes,  but why do you require it now as part of the vcpu topology change?

As-far-as-i-can-see, PPTT table changes(part of patch 5/9) do not require
this change. Change in Patch 5/9 has also been done in anticipation of
some future requirement(vcpu Hotplug?).

Please correct me here if I am wrong?

Thanks