Re: [PATCH 38/39] cpumask: Add enabled cpumask for present CPUs that can be brought online

Russell King (Oracle)
2023-10-24T16:05:56Z

On Tue, Oct 24, 2023 at 06:02:30PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Oct 24, 2023 at 04:19:24PM +0100, Russell King wrote:
> > From: James Morse <james.morse@arm.com>
> >
> > The 'offline' file in sysfs shows all offline CPUs, including those
> > that aren't present. User-space is expected to remove not-present CPUs
> > from this list to learn which CPUs could be brought online.
> >
> > CPUs can be present but not-enabled. These CPUs can't be brought online
> > until the firmware policy changes, which comes with an ACPI notification
> > that will register the CPUs.
> >
> > With only the offline and present files, user-space is unable to
> > determine which CPUs it can try to bring online. Add a new CPU mask
> > that shows this based on all the registered CPUs.
> >
> > Signed-off-by: James Morse <james.morse@arm.com>
> > ---
> > drivers/base/cpu.c | 10 ++++++++++
> > include/linux/cpumask.h | 25 +++++++++++++++++++++++++
> > kernel/cpu.c | 3 +++
> > 3 files changed, 38 insertions(+)
> >
> > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> > index 2b9cb2667654..f8bf1d4c7d71 100644
> > --- a/drivers/base/cpu.c
> > +++ b/drivers/base/cpu.c
> > @@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)
> > {
> > int logical_cpu = cpu->dev.id;
> >
> > + set_cpu_enabled(logical_cpu, false);
> > unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
> >
> > device_unregister(&cpu->dev);
> > @@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
> > }
> > static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
> >
> > +static ssize_t print_cpus_enabled(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_enabled_mask));
> > +}
> > +static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);
>
> This needs to be documented somewhere in Documentation/ABI/ did I miss
> that patch?

Thanks for pointing that out, no you missed the patch as nothing
touches Documentation/ABI/ in this patch series. I'll add some blurb
for it for the next iteration.

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