PCIe readout performance depending on kernel

I have a PCIe (Gen3) device that transfers data to the computer RAM in chunks of 256 MiB, each copy taking about 48 ms. I am using Ubuntu 20.04 and a kernel device module to handle the data transfer. Whenever I upgrade to a newer kernel, I recompile the driver.

I recently noticed that with image 5.8.0-53, the readout was consistent, and taking about 48ms (+/- 0.2 ms). After upgrading to 5.8.0-55 (same for -57 and -59), the operation takes 51 ms. The increase is not convenient as it’s a real time application and it should stay at or below 50ms in order not to lose data.

I was curious to know what might be the reason behind and if there is a changelog pointing at what changes might have caused this change, or if there is any way to give feedback via GitHub? Maybe it’s a regression and newer kernel versions have better performance? Thanks in advance for your advice.