Virtual Processor Folding

A simple and direct way to see which processors are active and which processors are not available due to “virtual processor folding” is the kernel debugger kdb.

The following command displays the desired information:

# echo vpm | kdb
...
VSD Thread State.
CPU  CPPR VP_STATE FLAGS SLEEP_STATE  PROD_TIME: SECS   NSECS     CEDE_LAT

   0     0  ACTIVE      0 AWAKE        0000000000000000  00000000  00  
   1     0  ACTIVE      0 AWAKE        0000000000000000  00000000  00  
   2     0  ACTIVE      0 AWAKE        0000000000000000  00000000  00  
   3     0  ACTIVE      0 AWAKE        0000000000000000  00000000  00  
   4     0  DISABLED    0 AWAKE        0000000000000000  00000000  00  
   5    11  DISABLED    0 SLEEPING     000000005D9F15BE  0F77D2C6  02  
   6    11  DISABLED    0 SLEEPING     000000005D9F15BE  0F77D0C8  02  
   7    11  DISABLED    0 SLEEPING     000000005D9F15BE  217D3F61  02  

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The output was created on a system with 2 processor cores and SMT4. CPUs 4-7 are currrently DISABLED, which is the second processor core.