Performance lost at interfaces mSATA, ETH, SPI when upgrade from 4.9 to 4.14

chameleon19

Hello,
for our project we are using a customized baseboard for a i.MX6Q (especially TQMa6Q from TQ-Group).
Therefore TQ provides for everyone a so called Board-Support-Package.
In the past we have several version in use.

A test with the Gigabit LAN interface has shown that the throughput (determined with iperf) of the kernel 4.14.141 is approx. 30-35% less than determined with the kernel 4.9.0.
There is also a performance loss in our test (with dd) of the mSATA SSD - approx. 30 % when writing and approx. 25 % when reading. Also with hdparm it is about 20-25 % less reading throughput.
The SPI-interface also has a 33% slower data exchange rate.
The used hardware was always identical, only the image on the SD card was different.
The tests were carried out with an already adapted carrier board (see point 1).

Does anyone know the cause? Because there must have been a significant change between Kernel 4.9 and 4.14!
Does anyone have a solution (patch, newer kernel, etc.) for us?

Thanks in advance.
BR
Rob