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List:       freebsd-hackers
Subject:    Re: About CPU cores numbering an processor affinity
From:       Ivan Voras <ivoras () freebsd ! org>
Date:       2013-08-26 11:42:38
Message-ID: kvfev7$e0r$1 () ger ! gmane ! org
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On 23/08/2013 15:23, Dmitry Sivachenko wrote:
> Hello!
> 
> I am using FreeBSD-9-STABLE on the following hardware:
> 
> FreeBSD/SMP: Multiprocessor System Detected: 24 CPUs
> FreeBSD/SMP: 2 package(s) x 6 core(s) x 2 SMT threads
> 
> So I have 2 physical CPUs with 6 core each.
> 
> # cpuset -g
> pid -1 mask: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, \
> 20, 21, 22, 23 
> 
> So each of 24 cores are numbered 0..23.
> 
> 1) In what particular order are these cores numbered?  Can I assume that 0..11 \
> correspond to 1st physical CPU and 12..23 to second?  How SMT threads are numbered \
> within each core?

You could look at the kern.sched.topology_spec sysctl, which outputs
like this:

<groups>
 <group level="1" cache-level="0">
  <cpu count="8" mask="ff">0, 1, 2, 3, 4, 5, 6, 7</cpu>
  <children>
   <group level="2" cache-level="2">
    <cpu count="4" mask="f">0, 1, 2, 3</cpu>
   </group>
   <group level="2" cache-level="2">
    <cpu count="4" mask="f0">4, 5, 6, 7</cpu>
   </group>
  </children>
 </group>
</groups>

Note that this output is created from the kernel's own interpretation of
the pysical CPUs, not necessarily from what the physical topology
actually is (but if there is a mismatch, it's a bug).


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