Problems running real time on a Dell Precision 5820

Hi all,

We are running a Linux preempt RT kernel (Linux 4.9.84-rt62) on a Dell with an Intel 8 core processor and we have some latency problems that hope its possible to get rid of.

When we tested our application we noticed some strange latency spikes of around 750µs and once in a while around 5000µs. Since our application is going to run in real-time with 4000Hz (250µs cycle time) those spikes are unacceptable to us, so we would like to know if it is possible for you to help us get rid of them (or if we have to run the application on another machine).

We have come so far so we have traced the cause of them to be SMI’s (system managed interrupts). The tools we used under Linux are, common in the real-time comunity, applications called cyclictest and hwlatdetect.

By running hwlatdetect we noticed that about once an hour we “lost” the processor to the SMI’s and our latency jumped up to 750µs and during long runs (for a day or more) we have found single spikes to 5000µs.

We have tried to change some of the BIOS settings that we thought could affect SMI’s but so far no luck, so now we are wondering if you have any input to us on this?

We are running the same system on a smaller Dell T3420 system with only 4 cores and it is running smoothly with acceptable latency.

The system is a Dell Precision 5820 Tower, BIOS 1.4.0.

We have been in contact with support but they only say that the kernel isn't supported, but as far as we can see, the problem isn't the kernel, its in the BIOS.