Speaking of Linux kernel network stack enhancements, there's one I'm interested in but not sure where to start.
I was trying to setup ECMP on Ubuntu 14 and found I was constantly getting TCP RST. Turns out after digging into the code I found the path selection algorithm is not a consistent hash of a packet header tuple but rather pseudo-randomly chosen.
In older kernels there was a route cache so a path would be chosen and cached and so you would get a stable ECMP route per source. The route cache was removed so now the random selection runs on every packet leading to unstable routing.
It seems a simple fix of choosing the right hash function and maybe adding some configuration flags to determine which fields are hashes on (typically 5-tuple SrcIP, DstIP, Ip Protocol, TCP Src Port, TCP Dst Port).
But what would be incredibly cool is if my patch could one day possibly even merge to mainline. Is it reasonable to just blast a 'here's what I'm trying' out to netdev mailing list to get some feedback? I must admit I'm a bit intimidated to post...
Absolutely go for it! Post it even if you feel uncertain about it, just be clear about that, and about what your patch is trying to achieve, when the unexpected behaviour happens, and try to include a way for others to reproduce/investigate (as simple as possible, perhaps a program that demonstrates the bug). Also be clear about how you feel about whether or not the patch is the right approach and about what you would like list members to do with it (are you looking to confirm that what you're seeing is a real kernel bug, or a misunderstanding, or an application bug, and/or are you looking for help solving the bug/issue you're seeing, and/or are you looking to get it merged, etc). Can you demonstrate/quantify how your patch improves/fixes things, etc.
Open source is generally quite kind to newbies, provided you provide that important context. Try to explain not just what you're doing, but also be very clear about why. Explain the problem as well as you can, and then discuss what solutions you've considered thus far.
It sounds like you have a good understanding of the problem. If anything, I'd look into why the route cache was removed; perhaps there was a good reason for this? If nothing else, you can ask and learn something.
I was trying to setup ECMP on Ubuntu 14 and found I was constantly getting TCP RST. Turns out after digging into the code I found the path selection algorithm is not a consistent hash of a packet header tuple but rather pseudo-randomly chosen.
In older kernels there was a route cache so a path would be chosen and cached and so you would get a stable ECMP route per source. The route cache was removed so now the random selection runs on every packet leading to unstable routing.
It seems a simple fix of choosing the right hash function and maybe adding some configuration flags to determine which fields are hashes on (typically 5-tuple SrcIP, DstIP, Ip Protocol, TCP Src Port, TCP Dst Port).
But what would be incredibly cool is if my patch could one day possibly even merge to mainline. Is it reasonable to just blast a 'here's what I'm trying' out to netdev mailing list to get some feedback? I must admit I'm a bit intimidated to post...