Re: [PATCH v5 03/18] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	"Russell King (Oracle)" <linux@armlinux.org.uk>,
	<linux-pm@vger.kernel.org>, <loongarch@lists.linux.dev>,
	<linux-acpi@vger.kernel.org>, <linux-arch@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <kvmarm@lists.linux.dev>,
	<x86@kernel.org>, Miguel Luis <miguel.luis@oracle.com>,
	James Morse <james.morse@arm.com>,
	Salil Mehta <salil.mehta@huawei.com>,
	"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>
Subject: Re: [PATCH v5 03/18] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()
Date: Wed, 17 Apr 2024 11:39:46 +0100	[thread overview]
Message-ID: <20240417113946.00000edb@Huawei.com> (raw)
In-Reply-To: <CAJZ5v0iK61_ihUZX_tXoSGdhpYDWFhEBbEuFf6WFiiD0QSeTDg@mail.gmail.com>

On Tue, 16 Apr 2024 21:02:02 +0200
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> 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?

Absolutely.  This needs cleaning up beyond this hack.

Given pr has been initialized to 0, flipping the flag to be something
like 'initialized' and having the driver set it on first online rather than
in acpi_processor.c will clean it up further.

Jonathan
> 
> > @@ -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!