Linux 3.7 Released

The wait is over; diegocg writes "Linux kernel 3.7 has been released. This release adds support for the new ARM 64-bit architecture, ARM multiplatform — the ability to boot into different ARM systems using a single kernel; support for cryptographically signed kernel modules; Btrfs support for disabling copy-on-write on a per-file basis using chattr; faster Btrfs fsync(); a new experimental 'perf trace' tool modeled after strace; support for the TCP Fast Open feature in the server side; experimental SMBv2 protocol support; stable NFS 4.1 and parallel NFS; a vxlan tunneling protocol that allows to transfer Layer 2 ethernet packets over UDP; and support for the Intel SMAP security feature. Many small features and new drivers and fixes are also available. Here's the full list of changes."

Comments

Re:UDP ...

[vlm]

Why does vxlan transfer L2 packets using UDP and not TCP? I have also seen this on other L2 protocols like L2TP and PPTP ... just curious ...

TCP has a feedback loop when packets are lost... So you'd have that at both layers, the actual session and the tunnel.

Its an engineering thing where if you embed a feedback loop inside a feedback loop, things will be OK if you're VERY careful but most are not and you'll make a lovely oscillator and just blow it all to bits.

Fundamentally, UDP doesn't guarantee delivery so its OK to shove it inside UDP, and TCP has its own repair mechanism so you don't need to guarantee its sub-layers, so its not like you're missing anything.

Finally it just kills performance because TCP loves big buffers for each connection so you need megatons of ram until you start dropping packets and letting TCP police itself. Which meanwhile results in horrific latency. But if you tunnel over UDP, you don't really need much of a buffer on the tunneler itself and you'll overall end up with better latency specs. So its cheaper and works better. Hard to beat that combo...