EMR: CLOCKTICKS changes significantly when using P2P_CRD_OCCUPANCY

Hi,

I am studying peer-to-peer (P2P) traffic on an Intel Xeon Scalable Processor (Gold 6526Y). In the background, an application triggers P2P data transfers from IIO_8 to IIO_1 (within the same socket, S1). I am trying to analyze P2P credits.

From the [document](https://www.intel.com/content/www/us/en/content-details/817509/5th-gen-intel-xeon-scalable-processor-xcc-codename-emerald-rapids-uncore-performance-monitoring-guide.html), I found 2 counters:

`UNC_M2P_P2P_CRD_OCCUPANCY.LOCAL_NCB` (on page 275):

`CLOCKTICKS` (on page 282. I did not find this counter listed in [emeraldrapids_uncore_experimental.json](https://github.com/intel/perfmon/blob/main/EMR/events/emeraldrapids_uncore_experimental.json)):

The workload remains unchanged, but when I run the two commands below (`uncore_m2pcie_1` is the receiver side), the reported number of clock ticks differs:

``` shell
~$ sudo perf stat -a --per-socket -e 'uncore_m2pcie_1/event=0x1/' -e 'uncore_m2pcie_1/event=0x14,umask=0x01/' -- sleep 1

Performance counter stats for 'system wide':

S0 1 4,555 uncore_m2pcie_1/event=0x1/
S0 1 0 uncore_m2pcie_1/event=0x14,umask=0x01/
S1 1 3,960 uncore_m2pcie_1/event=0x1/
S1 1 185,547,916,227 uncore_m2pcie_1/event=0x14,umask=0x01/

1.000726843 seconds time elapsed

~$ sudo perf stat -a --per-socket -e 'uncore_m2pcie_1/event=0x1/' -- sleep 1

Performance counter stats for 'system wide':

S0 1 2,501,812,075 uncore_m2pcie_1/event=0x1/
S1 1 2,501,845,625 uncore_m2pcie_1/event=0x1/

1.000719858 seconds time elapsed
```

The same issue happens on the sender side, when using CLOCKTICKS and UNC_M2P_TxC_CREDITS.PRQ simultaneously.

``` shell
~$ sudo perf stat -a --per-socket -e 'uncore_m2pcie_8/event=0x1/' -- sleep 1

Performance counter stats for 'system wide':

S0 1 2,501,877,387 uncore_m2pcie_8/event=0x1/
S1 1 2,501,879,920 uncore_m2pcie_8/event=0x1/

1.000734614 seconds time elapsed

~$ sudo perf stat -a --per-socket -e 'uncore_m2pcie_8/event=0x1/' -e 'uncore_m2pcie_8/event=0x2d,umask=0x01/' -- sleep 1

Performance counter stats for 'system wide':

S0 1 5,345 uncore_m2pcie_8/event=0x1/
S0 1 2,501,815,830 uncore_m2pcie_8/event=0x2d,umask=0x01/
S1 1 4,688 uncore_m2pcie_8/event=0x1/
S1 1 1,247,844,120 uncore_m2pcie_8/event=0x2d,umask=0x01/

1.000703356 seconds time elapsed
```

From my understanding, `CLOCKTICKS` shows the number of clock cycles during the monitoring interval. I don't understand why they vary this significantly.