Implement sched_[gs]etaffinity()
Mark Geisert
mark@maxrnd.com
Fri Apr 26 08:44:00 GMT 2019
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
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