Server Gurus Discussions

[f_popchenko]

Hello!

I'm working with AMD Epyc 7301 (AMD64 Family 17h model 00h-0Fh) with QNX (real-time OS) and have SMI interruptions on all CPUs every 32 ms for ~400 us. But in Linux (SLES RT) i dont't see such behaviour and the SMI counter in MSR results 0. I've read Performance Tuning Guidelines for Low Latency Response on AMD EPYC™-Based Servers Application Note and perform all BIOS optimization to decrease or remove SMIs, but it didn't work in this case. 

So, I have some questions:

1. Is there a way to disable SMI or sources of SMI in MSR or other specific registers, that I can write from OS?

2. Do you have any suggestions what can be a reason for such behaviour?

3. In case if you known with this promlem, what should I do to reduse SMIs in QNX like it works in Linux?

[f_popchenko]

In case that someone face the same problem. 

There is an SMI register space describred in BIOS and Kernel Developer’s Guide (BKDG) for AMD Family 16h Models 00h-0Fh Processors doc on p. 875. And I found SMI Enable bit in SMITRIG0 register. Setting this bit disables SMI. Also there is a possibility to disable SMI sources.

[djselbeck]

Hello,

I observed a similar behavior. I am using a Supermicro AS -1023US-TR4 Server with two AMD Epyc 7501. I am doing operating systems research. However, I think you need to read the SMI count out of the PMC registers. Reading of SMI count is (as far as I know only supported on non-AMD AMD64 platforms). You can configure a PMC to count SMIs, I am doing this and get reliable information when SMIs occured. Sadly they occur really often and polute my measurements quite often.