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

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  Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[]  array to store persistent cpuid <-> apicid mapping. Tang Chen <tangchen@cn.fujitsu.com> - 2015-09-26 12:00 +0200
    Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce  apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping. Tejun Heo <tj@kernel.org> - 2015-09-26 20:00 +0200
      Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[]  array to store persistent cpuid <-> apicid mapping. Tang Chen <tangchen@cn.fujitsu.com> - 2015-09-28 04:00 +0200

#1233184 — Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping.

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.
>

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#1233252 — Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping.

On Sat, Sep 26, 2015 at 05:52:09PM +0800, Tang Chen wrote:
> >>+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.

If the above condition can happen, the original code should have had a
similar check as above, right?  Sure, max_logical_cpuid is a new thing
but that doesn't seem to change whether the above condition can happen
or not, no?

Thanks.

-- 
tejun
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#1233814

On 09/27/2015 01:56 AM, Tejun Heo wrote:
> On Sat, Sep 26, 2015 at 05:52:09PM +0800, Tang Chen wrote:
>>>> +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.
> If the above condition can happen, the original code should have had a
> similar check as above, right?  Sure, max_logical_cpuid is a new thing
> but that doesn't seem to change whether the above condition can happen
> or not, no?

Right, indeed. It is in

generic_processor_info()
|--> if (num_processors >= nr_cpu_ids)

Will remove my new added check.

Thanks.

>
> Thanks.
>

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