Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping.

[Tang Chen]

Hi tj,

On 09/11/2015 03:55 AM, Tejun Heo wrote:
> Hello,
>
> So, overall, I think this is the right way to go although I have no
> idea whether the acpi part is okay.

Thank you very much for reviewing. :)

> > +/*
> > + * Current allocated max logical CPU ID plus 1.
> > + * All allocated CPU ID should be in [0, max_logical_cpuid),
> > + * so the maximum of max_logical_cpuid is nr_cpu_ids.
> > + *
> > + * NOTE: Reserve 0 for BSP.
> > + */
> > +static int max_logical_cpuid = 1;
> Rename it to nr_logical_cpuids and just mention that it's allocated
> contiguously?

OK.

> > +static int cpuid_to_apicid[] = {
> > +	[0 ... NR_CPUS - 1] = -1,
> > +};
> And maybe mention how the two variables are synchronized?

User should call allocate_logical_cpuid() to get a new logical cpuid.
This allocator will ensure the synchronization.

Will mention it in the comment.

> > +static int allocate_logical_cpuid(int apicid)
> > +{
> > +	int i;
> > +
> > +	/*
> > +	 * cpuid <-> apicid mapping is persistent, so when a cpu is up,
> > +	 * check if the kernel has allocated a cpuid for it.
> > +	 */
> > +	for (i = 0; i < max_logical_cpuid; i++) {
> > +		if (cpuid_to_apicid[i] == apicid)
> > +			return i;
> > +	}
> > +
> > +	/* Allocate a new cpuid. */
> > +	if (max_logical_cpuid >= nr_cpu_ids) {
> > +		WARN_ONCE(1, "Only %d processors supported."
> > +			     "Processor %d/0x%x and the rest are ignored.\n",
> > +			     nr_cpu_ids - 1, max_logical_cpuid, apicid);
> > +		return -1;
> > +	}
> So, the original code didn't have this failure mode, why is this
> different for the new code?

It is not different. Since max_logical_cpuid is new, this is ensure it 
won't
go beyond NR_CPUS.

Thanks.

> Thanks.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/