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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Tue, 16 Apr 2024 21:02:02 +0200
Message-ID: <CAJZ5v0iK61_ihUZX_tXoSGdhpYDWFhEBbEuFf6WFiiD0QSeTDg@mail.gmail.com>
Subject: Re: [PATCH v5 03/18] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, 
	"Russell King (Oracle)" <linux@armlinux.org.uk>, linux-pm@vger.kernel.org, loongarch@lists.linux.dev, 
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	kvmarm@lists.linux.dev, x86@kernel.org, Miguel Luis <miguel.luis@oracle.com>, 
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	Jean-Philippe Brucker <jean-philippe@linaro.org>, Catalin Marinas <catalin.marinas@arm.com>, 
	Will Deacon <will@kernel.org>, linuxarm@huawei.com, justin.he@arm.com, 
	jianyong.wu@arm.com
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On Tue, Apr 16, 2024 at 7:41=E2=80=AFPM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Mon, 15 Apr 2024 13:23:51 +0100
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
>
> > On Mon, 15 Apr 2024 14:04:26 +0200
> > "Rafael J. Wysocki" <rafael@kernel.org> wrote:

[cut]

> > > > I'm still very much stuck on the hotadd_init flag however, so any s=
uggestions
> > > > on that would be very welcome!
> > >
> > > I need to do some investigation which will take some time I suppose.
> >
> > I'll do so as well once I've gotten the rest sorted out.  That whole
> > structure seems overly complex and liable to race, though maybe suffici=
ent
> > locking happens to be held that it's not a problem.
>
> Back to this a (maybe) last outstanding problem.
>
> Superficially I think we might be able to get around this by always
> doing the setup in the initial online. In brief that looks something the
> below code.  Relying on the cpu hotplug callback registration calling
> the acpi_soft_cpu_online for all instances that are already online.
>
> Very lightly tested on arm64 and x86 with cold and hotplugged CPUs.
> However this is all in emulation and I don't have access to any significa=
nt
> x86 test farms :( So help will be needed if it's not immediately obvious =
why
> we can't do this.

AFAICS, this should work.  At least I don't see why it wouldn't.

> Of course, I'm open to other suggestions!
>
> For now I'll put a tidied version of this one is as an RFC with the rest =
of v6.
>
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.=
c
> index 06e718b650e5..97ca53b516d0 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -340,7 +340,7 @@ static int acpi_processor_get_info(struct acpi_device=
 *device)
>          */
>         per_cpu(processor_device_array, pr->id) =3D device;
>         per_cpu(processors, pr->id) =3D pr;
> -
> +       pr->flags.need_hotplug_init =3D 1;
>         /*
>          *  Extra Processor objects may be enumerated on MP systems with
>          *  less than the max # of CPUs. They should be ignored _iff
> diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_dri=
ver.c
> index 67db60eda370..930f911fc435 100644
> --- a/drivers/acpi/processor_driver.c
> +++ b/drivers/acpi/processor_driver.c
> @@ -206,7 +206,7 @@ static int acpi_processor_start(struct device *dev)
>
>         /* Protect against concurrent CPU hotplug operations */
>         cpu_hotplug_disable();
> -       ret =3D __acpi_processor_start(device);
> +       //      ret =3D __acpi_processor_start(device);
>         cpu_hotplug_enable();
>         return ret;
>  }

So it looks like acpi_processor_start() is not necessary any more, is it?

> @@ -279,7 +279,7 @@ static int __init acpi_processor_driver_init(void)
>         if (result < 0)
>                 return result;
>
> -       result =3D cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +       result =3D cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>                                            "acpi/cpu-drv:online",
>                                            acpi_soft_cpu_online, NULL);
>         if (result < 0)
> >
> > Jonathan

Thanks!