pcm indicates that the UPI rate of the SPR CPU is not 16.0GT/s. This is inconsistent with the register information
Yo1ick opened this issue · 3 comments
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
I'll let Roman answer this, he knows better how this is programmed and how it may come to such weird discrepancies.
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.