Adding support for kernel scheduler topology for multi socket systems. Attached patch is tested on an AMD EPYC 2P system.
Default :
sysctl kern.sched.topology_spec command on a 2P EPYC system gives the following topology
kern.sched.topology_spec: <groups>
<group level="1" cache-level="0">
<cpu count="128" mask="ffffffffffffffff,ffffffffffffffff,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127</cpu>
<children>
<group level="2" cache-level="0">
<cpu count="16" mask="ffff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15</cpu>
<children>
<group level="3" cache-level="3">
<cpu count="8" mask="ff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7</cpu>
<children>
<group level="4" cache-level="2">
<cpu count="2" mask="3,0,0,0">0, 1</cpu>
<flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
....
with the new patch the topology is as below
kern.sched.topology_spec: <groups>
<group level="1" cache-level="0">
<cpu count="128" mask="ffffffffffffffff,ffffffffffffffff,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127</cpu>
<children>
<group level="2" cache-level="0">
<cpu count="64" mask="ffffffffffffffff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63</cpu>
<children>
<group level="3" cache-level="0">
<cpu count="16" mask="ffff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15</cpu>
<children>
<group level="4" cache-level="3">
<cpu count="8" mask="ff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7</cpu>
<children>
<group level="5" cache-level="2">
<cpu count="2" mask="3,0,0,0">0, 1</cpu>
<flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>