From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: 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,
linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev,
x86@kernel.org, acpica-devel@lists.linuxfoundation.org,
linux-csky@vger.kernel.org, linux-doc@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
Salil Mehta <salil.mehta@huawei.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
jianyong.wu@arm.com, justin.he@arm.com,
James Morse <james.morse@arm.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>
Subject: Re: [PATCH RFC v4 02/15] ACPI: processor: Register all CPUs from acpi_processor_get_info()
Date: Tue, 20 Feb 2024 11:27:15 +0000 [thread overview]
Message-ID: <ZdSMk93c1I6x973h@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAJZ5v0iiJpUWq5GMSnKFWQTzn_bdwoQz9m=hDaXNg4Lj_ePF4g@mail.gmail.com>
On Thu, Feb 15, 2024 at 08:22:29PM +0100, Rafael J. Wysocki wrote:
> On Wed, Jan 31, 2024 at 5:50 PM Russell King <rmk+kernel@armlinux.org.uk> wrote:
> > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > index cf7c1cca69dd..a68c475cdea5 100644
> > --- a/drivers/acpi/acpi_processor.c
> > +++ b/drivers/acpi/acpi_processor.c
> > @@ -314,6 +314,18 @@ static int acpi_processor_get_info(struct acpi_device *device)
> > cpufreq_add_device("acpi-cpufreq");
> > }
> >
> > + /*
> > + * Register CPUs that are present. get_cpu_device() is used to skip
> > + * duplicate CPU descriptions from firmware.
> > + */
> > + if (!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > + !get_cpu_device(pr->id)) {
> > + int ret = arch_register_cpu(pr->id);
> > +
> > + if (ret)
> > + return ret;
> > + }
> > +
> > /*
> > * Extra Processor objects may be enumerated on MP systems with
> > * less than the max # of CPUs. They should be ignored _iff
>
> This is interesting, because right below there is the following code:
>
> if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> int ret = acpi_processor_hotadd_init(pr);
>
> if (ret)
> return ret;
> }
>
> and acpi_processor_hotadd_init() essentially calls arch_register_cpu()
> with some extra things around it (more about that below).
>
> I do realize that acpi_processor_hotadd_init() is defined under
> CONFIG_ACPI_HOTPLUG_CPU, so for the sake of the argument let's
> consider an architecture where CONFIG_ACPI_HOTPLUG_CPU is set.
>
> So why are the two conditionals that almost contradict each other both
> needed? It looks like the new code could be combined with
> acpi_processor_hotadd_init() to do the right thing in all cases.
>
> Now, acpi_processor_hotadd_init() does some extra things that look
> like they should be done by the new code too.
>
> 1. It checks invalid_phys_cpuid() which appears to be a good idea to me.
>
> 2. It uses locking around arch_register_cpu() which doesn't seem
> unreasonable either.
>
> 3. It calls acpi_map_cpu() and I'm not sure why this is not done by
> the new code.
>
> The only thing that can be dropped from it is the _STA check AFAICS,
> because acpi_processor_add() won't even be called if the CPU is not
> present (and not enabled after the first patch).
>
> So why does the code not do 1 - 3 above?
Honestly, I'm out of my depth with this and can't answer your
questions - and I really don't want to try fiddling with this code
because it's just too icky (even in its current form in mainline)
to be understandable to anyone who hasn't gained a detailed knowledge
of this code.
It's going to require a lot of analysis - how acpi_map_cpuid() behaves
in all circumstances, what this means for invalid_logical_cpuid() and
invalid_phys_cpuid(), what paths will be taken in each case. This code
is already just too hairy for someone who isn't an experienced ACPI
hacker to be able to follow and I don't see an obvious way to make it
more readable.
James' additions make it even more complex and less readable.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
next prev parent reply other threads:[~2024-02-20 11:27 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-31 16:48 [RFC PATCH v4 00/15] ACPI/arm64: add support for virtual cpu hotplug Russell King (Oracle)
2024-01-31 16:49 ` [PATCH RFC v4 01/15] ACPI: Only enumerate enabled (or functional) processor devices Russell King
2024-01-31 17:25 ` Miguel Luis
2024-02-15 20:10 ` Rafael J. Wysocki
2024-02-19 9:45 ` Jonathan Cameron
2024-02-20 11:30 ` Russell King (Oracle)
2024-02-21 13:01 ` Rafael J. Wysocki
2024-01-31 16:49 ` [PATCH RFC v4 02/15] ACPI: processor: Register all CPUs from acpi_processor_get_info() Russell King
2024-02-15 19:22 ` Rafael J. Wysocki
2024-02-20 11:27 ` Russell King (Oracle) [this message]
2024-02-20 15:13 ` Russell King (Oracle)
2024-02-20 16:24 ` Jonathan Cameron
2024-02-20 19:59 ` Rafael J. Wysocki
2024-02-21 12:04 ` Rafael J. Wysocki
2024-02-20 20:59 ` Thomas Gleixner
2024-03-22 18:53 ` Jonathan Cameron
2024-04-10 12:43 ` Jonathan Cameron
2024-04-10 13:28 ` Rafael J. Wysocki
2024-04-10 13:50 ` Jonathan Cameron
2024-04-10 14:19 ` Rafael J. Wysocki
2024-04-10 15:58 ` Jonathan Cameron
2024-04-10 18:56 ` Russell King (Oracle)
2024-04-10 19:08 ` Rafael J. Wysocki
2024-04-10 21:07 ` Jonathan Cameron
2024-01-31 16:49 ` [PATCH RFC v4 03/15] ACPI: Move acpi_bus_trim_one() before acpi_scan_hot_remove() Russell King
2024-01-31 16:49 ` [PATCH RFC v4 04/15] ACPI: Rename acpi_processor_hotadd_init and remove pre-processor guards Russell King
2024-01-31 16:50 ` [PATCH RFC v4 05/15] ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug Russell King
2024-01-31 16:50 ` [PATCH RFC v4 06/15] ACPI: convert acpi_processor_post_eject() to use IS_ENABLED() Russell King (Oracle)
2024-01-31 16:50 ` [PATCH RFC v4 07/15] ACPI: Check _STA present bit before making CPUs not present Russell King
2024-01-31 16:50 ` [PATCH RFC v4 08/15] ACPI: Warn when the present bit changes but the feature is not enabled Russell King
2024-01-31 16:50 ` [PATCH RFC v4 09/15] arm64: acpi: Move get_cpu_for_acpi_id() to a header Russell King
2024-01-31 16:50 ` [PATCH RFC v4 10/15] irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc() Russell King
2024-02-02 16:44 ` Jonathan Cameron
2024-01-31 16:50 ` [PATCH RFC v4 11/15] irqchip/gic-v3: Add support for ACPI's disabled but 'online capable' CPUs Russell King
2024-02-02 16:47 ` Jonathan Cameron
2024-01-31 16:50 ` [PATCH RFC v4 12/15] arm64: psci: Ignore DENIED CPUs Russell King
2024-04-11 11:35 ` Jonathan Cameron
2024-04-11 13:25 ` Jonathan Cameron
2024-01-31 16:50 ` [PATCH RFC v4 13/15] ACPI: add support to (un)register CPUs based on the _STA enabled bit Russell King
2024-01-31 16:50 ` [PATCH RFC v4 14/15] arm64: document virtual CPU hotplug's expectations Russell King
2024-02-02 17:04 ` Jonathan Cameron
2024-01-31 16:50 ` [PATCH RFC v4 15/15] cpumask: Add enabled cpumask for present CPUs that can be brought online Russell King
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