Click Kernel does not really work anymore

[tbarbette]

As one of the first step to try to get FastClick more open and properly maintained by the community, I'd like to fix the Kernel mode.

With the last patch, it is compiling on up to 4.4. However recent kernel crashes, I think it's due to the last changes by Eddie in the scheduling, among them the recent issues mentioned there : kohler/click#407 . @pallas @peterhurley did you experience this kind of problem with a recent merge?

In a more long-term, I think we can bring back Kernel Click in the front stage if, instead of using the rx_handler we used the xdp_handler. One can hijack this one to not use eBPF but eg a Click function. This allows to completely byoass the kernel stack functions, including the heavy sk_buff creation step - which is mostly useless for a Click program - and achieve speed comparable to what DPDK proposes, but in-kernel. Looking at the ixgbe driver, the XDP buffers are safe to keep as the ring bucket will be re-mapped to some new buffer in the DMA zone, so for this kind of driver we do not even need to remap or copy the buffers. If some people are still looking into Kernel Click, this would probably be the biggest performance improvement for Kernel Click in years.