Re: [PATCH 1/5] x86/smpboot: Add the missing description of possible_cpus

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

At 03/21/2018 05:34 PM, Dou Liyang wrote:
> Hi Peter,
> 
> At 03/21/2018 05:08 PM, Peter Zijlstra wrote:
>> On Wed, Mar 21, 2018 at 01:33:24PM +0800, Dou Liyang wrote:
>>> How about:
>>>
>>> possible_cpus=    [s390,x86_64] Set the number of possible CPUs which
>>>         are determined by the ACPI tables MADT or mptables by
>>>         default. possible_cpus=n : n >= 1 enforces the possible
>>>         number to be 'n'.
>>>         While nr_cpus is also be set: nr_cpus=m, choice the
>>>         minimum one for the number of possible CPUs.
>>
>> So what is the exact difference between possible_cpus and nr_cpus ? I
> 
> the possible_cpus= can reset the number of possible CPUs, even bigger
> than 'num_processors + disabled_cpus', But nr_cpus= can't.
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       the maximum number kernel gets from ACPI/mptables, no matter what
number nr_cpus= is, the number of possible CPUs will not bigger than it.

>
>> konw maxcpus= limits the number of CPUs we bring up, and possible_cpus
>> limits the possible_map, but I'm not entirely sure what nr_cpus does
>> here.
>>
> 
> nr_cpus can limited the maximum CPUs that the kernel could support.
> 
> Here is a double check in case of using them at the same time, even if I
> think just using possible_cpus= is enough. :-)
> 
> Thanks,
>      dou.
>>
>>