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SubjectRe: [PATCH v5 03/18] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()
On Tue, Apr 16, 2024 at 7:41 PM 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 suggestions
> > > > 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 sufficient
> > 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 significant
> 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) = device;
> per_cpu(processors, pr->id) = pr;
> -
> + pr->flags.need_hotplug_init = 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_driver.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 = __acpi_processor_start(device);
> + // ret = __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 = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> + result = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> "acpi/cpu-drv:online",
> acpi_soft_cpu_online, NULL);
> if (result < 0)
> >
> > Jonathan

Thanks!

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