Implement sched_[gs]etaffinity()

[Mark Geisert]

On Wed, 17 Apr 2019, Corinna Vinschen wrote:
> On Apr 16 21:31, Mark Geisert wrote:
>> On Tue, 16 Apr 2019, Corinna Vinschen wrote:
>>> On Apr 16 01:19, Mark Geisert wrote:
>>>>   Anybody know if one can
>>>> depend on the group membership of the first processor group to apply to all
>>>> groups?
>>>
>>> Maybe https://go.microsoft.com/fwlink/p/?linkid=147914 helps?
>>>
>>> "If the number of logical processors exceeds the maximum group size,
>>>  Windows creates multiple groups by splitting the node into n groups,
>>>  where the first n-1 groups have capacities that are equal to the group
>>>  size."
>>
>> Great; thanks for that.
>>
>>> [...]
>>> Therefore:
>>>
>>>  WORD cpu_group = cpu_number / num_cpu_per_group;
>>>  KAFFINITY cpu_mask = 1L << (cpu_number % num_cpu_per_group);
>>>
>>> That also means the transposition between the groupless linux system
>>> and the WIndows system is fairly easy.
>>
>> Yes, dealing with an array of unsigned longs vs bitblt ops FTW.

I've been doing research to more fully understand the non-symmetric API 
for Windows affinity ops.  I came across a non-MS document online that 
discusses affinity on Windows with >64 CPUs.  The author works on "Process 
Lasso", a product that attempts to balance performance of apps across 
CPUs.

Anyway, he says processors are divided evenly among groups.  One reason 
for this is that Windows allocates new processes round-robin among the 
processor groups.  This won't balance properly if some groups have more 
processors than other groups.  Here's a link to the doc:
https://bitsum.com/general/the-64-core-threshold-processor-groups-and-windows/

I'm not trying to muddy the waters, I'm just trying to figure out if there 
are different processor group assignment methods for different kinds of 
systems, SMP vs NUMA for instance.

I don't think the code I've got is robust enough to submit yet.  I suppose 
I could ship what should work, i.e., single-group processes and threads 
and just return ENOSYS for multi-group ops.  Or just hold off 'til done.

..mark