I often hear tales about High Frequency shops using network cards which do kernel bypass. However, I also often hear about them using operating systems where they "tune" the kernel. If they are bypassing the kernel, do they need to tune the kernel?

Is it a case of they do both because whilst the network packets will bypass the kernel due to the card, there is still all the other stuff going on which tuning the kernel would help? So in other words, they use both approaches, one is just to speed up network activity and the other makes the OS generally more responsive/faster?

I ask because a friend of mine who works within this industry once said they don't really bother with kernel tuning anymore-because they use kernel bypass network cards? This didn't make too much sense as I thought you would always want a faster kernel for all the CPU-offloaded calculations.