Linux 3.13 [https://lkml.org/lkml/2014/1/19/148 was released] on Sun, 19 Jan 2014.
Summary: This release includes nftables, the successor of iptables, a revamp of the block layer designed for high-performance SSDs, a power capping framework to cap power consumption in Intel RAPL devices, improved squashfs performance, AMD Radeon power management enabled by default and automatic Radeon GPU switching, improved NUMA performance, improved performance with hugepage workloads, TCP Fast Open enabled by default, support for NFC payments, support for the High-availability Seamless Redundancy protocol, new drivers and many other small improvements.
1. Prominent features
1.1. A scalable block layer for high performance SSD storage
Traditional hard disks have defined for decades the designs that operating systems use to communicate applications with the storage device drivers. With the advent of modern solid-state disks (SSD), past assumptions are no longer valid. Linux had a single coarse lock design for protecting the IO request queue, which can achieve an IO submission rate of around 800.000 IOs per second, regardless of how many cores are used to submit IOs. This was more than enough for traditional magnetic hard disks, whose IO submission rate in random accesses is in the hundreds, but it has become not enough for the most advanced SSD disks, which can achieve a rate close to 1 million, and are improving fast with every new generation. It is also unfit for the modern multicore world.
This release includes a new design for the Linux block layer, based on two levels of queues: one level of per-CPU queues for submitting IO, which then funnel down into a second level of hardware submission queues. The mapping between submission queues and hardware queues might be 1:1 or N:M, depending on hardware support and configuration. Experiments shown that this design can achieve many millions of IOs per second, leveraging the new capabilities of NVM-Express or high-end PCI-E devices and multicore CPUs, while still providing the common interface and convenience features of the block layer.
Paper: [http://kernel.dk/blk-mq.pdf Linux Block IO: Introducing Multi-queue SSD Access on Multi-core Systems]
Recommended LWN article: [https://lwn.net/Articles/552904/ The multiqueue block layer]
1.2. nftables, the successor of iptables
iptables has a number of limitations both at the functional and code design level, problems with the system update rules and code duplication, which cause problems for code maintenance and for users. nftables is a new packet filtering framework that solves these problems, while providing backwards compatibility for current iptable users.
The core of the nftables design is a simple pseudo-virtual machine inspired in BPF. A [http://git.netfilter.org/nftables/ userspace utility] interprets the rule-set provided by the user, it compiles it to pseudo-bytecode and then it transfers it to the kernel. This approach can replace thousands of lines of code, since the bytecode instruction set can express the packet selectors for all existing protocols. Because the userspace utility parses the protocols to bytecode, it is no longer necessary a specific extension in kernel-space for each match, which means that users are likely not need to upgrade the kernel to obtain new matches and features, userspace upgrades will provide them. There is also [http://git.netfilter.org/libnftables/ a new library] for utilities that need to interact with the firewall.
nftables provides backwards iptables compatibility. There are [http://git.netfilter.org/iptables-nftables/ new iptables/iptables utilities] that translate iptables rules to nftables bytecode, and it is also possible to use and add new xtable modules. As a bonus, these new utilities provide features that weren't possible with the old iptables design: notification for changes in tables/chains, better incremental rule update support, and the ability to enable/disable the chains per