The _PERF_COUNTER_DATA structure is used in the counter header block.

 typedef struct _PERF_COUNTER_DATA {
   unsigned long dwDataSize;
   unsigned long dwSize;
 } PERF_COUNTER_DATA,
  *PPERF_COUNTER_DATA;

dwDataSize: The size, in bytes, of the performance counter data.

dwSize: The size, in bytes, of the structure and performance counter data.