pcm indicates that the UPI rate of the SPR CPU is not 16.0GT/s. This is inconsistent with the register information

[Yo1ick]

The compiled pcm tool reads the UPI rate information of the inel SPR CPU in debian. The UPI rate is 17.0GT/s with a low probability. If used together
Lspci - XXXX -s 7 e: 01.2 | grep -i 2 e0
2e0: 03 00 00 00 00 00 00 00 00 00 00 0 (Display 03 as 16GT/s)

Reading the CPU information increases the probability of firing. On my side, the probability of firing simultaneously is 0.014%. Sometimes the UPI displays 15.9GT/s8.2GT/s.
Tool version: Intel(r) Performance Counter Monitor (2023-02-14 09:00:31 +0100 ID=a2ac6af4)
[screenshot：]
[2023-05-29 16:32:36] ret13 2e0: 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[2023-05-29 16:32:36] ret23 130: 00 10 00 00 10 12 00 00 00 00 00 00 00 00 00 00
[2023-05-29 16:32:36] ret33 140: 00 00 a0 00 00 00 00 00 17 80 01 10 00 00 00 00
[2023-05-29 16:32:36] Socket 0
[2023-05-29 16:32:36] Max UPI link 0 speed: 35.8 GBytes/second (16.0 GT/second)
[2023-05-29 16:32:36] Max UPI link 1 speed: 35.8 GBytes/second (16.0 GT/second)
[2023-05-29 16:32:36] Max UPI link 2 speed: 35.8 GBytes/second (16.0 GT/second)
[2023-05-29 16:32:36] Socket 1
[2023-05-29 16:32:36] Max UPI link 0 speed: 35.8 GBytes/second (16.0 GT/second)
[2023-05-29 16:32:36] Max UPI link 1 speed: 35.8 GBytes/second (16.0 GT/second)
[2023-05-29 16:32:36] Max UPI link 2 speed: 38.0 GBytes/second (17.0 GT/second)
[2023-05-29 16:32:36]
[2023-05-29 16:32:36] Detected Intel(R) Xeon(R) Platinum 8457C "Intel(r) microarchitecture codename Sapphire Rapids-SP" stepping 6 microcode level 0x2b000461
[2023-05-29 16:32:36] ret14 2e0: 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[2023-05-29 16:32:36] ret24 130: 00 10 00 00 10 12 00 00 00 00 00 00 00 00 00 00
[2023-05-29 16:32:36] ret34 140: 00 00 00 00 00 00 00 00 17 80 01 00 00 00 00 00
By the way, what is the UPI rate calculated by pcm? Thank you

[ogbrugge]

I'll let Roman answer this, he knows better how this is programmed and how it may come to such weird discrepancies.

[rdementi]

On SPR PCM measures the UPI clock ticks performance monitoring event for a short fixed duration of time to compute UPI speed. Depending on the system load this can be not 100% precise due to OS scheduling. Please let us know if you are aware of a documented public register where the UPI speed information can be read on SPR.