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Networking

Support for the experimental Tail Loss Probe (TLP) algorithm improves the efficiency with which the TCP stack now handles lost packets at the end of a TCP transaction. The concept behind TLP and the Linux implementation are the products of work by developers at Google. According to measurements given in the commit comments, for short transactions, TLP should reduce retransmission timeouts by 15 per cent and shorten HTTP response times by an average of 6 per cent. Details of how it works can be found in the commit comments and in the TCP Maintenance Working Group's internet draft on TLP.

The kernel now supports the IEEE 802.1ad specification. The procedure, also known as VLAN stacking or QinQ, can be used to insert multiple VLAN tags into a single Ethernet frame. The relevant network settings are configured using the tool "ip".

Kernel Log penguin Drivers

Linux 3.10 sees the merging of drivers for USB 2.0 network chip RTL8152 and 11n wireless chip RTL8188EE, both from Realtek (1, 2, and others). The brcmsmac driver for the latest Broadcom chips can now run in access-point mode. Support for IPv6 in the driver for network connections over FireWire has been significantly improved. The input subsystem now includes a driver for the infrared receiver which Apple has been building into its computers for many years. There is also a new driver for the Roccat Kone Pure gaming mouse and the same manufacturer's IskuFX keyboard.

Infrastructure

The kernel developers have modified code designed to protect Samsung laptops from defects. The changes mean that the previously sometimes over-eager protection feature, which had occasionally blocked machines from other manufacturers from setting or modifying UEFI variables, will swing into action less frequently. A recent test by c't magazine, for example, found that several test machines were missing UEFI entries for booting the installed Linux OS following UEFI Linux installation, due to UEFI entry creation having been blocked by the older protection mechanism.

Linux can now slow the timer interrupt for individual CPU cores, which normally fires 100, 250 or 1000 times per second, to just one interrupt per second. This should prevent response time jitter on real-time systems and provide a small performance boost for high performance computing setups (1, 2, 3, 4, 5, and others). Timer interrupts cannot, however, be slowed on the CPU core used as boot strap processor (BSP/CPU#0). In addition, this feature only works on cores configured to run only a single process.

Virtualisation

The cpufreq subsystem, which controls changes to processor clock speed, now has basic support for ARM's big.LITTLE concept. This involves processors containing both fast, power-hungry cores and much slower, more power efficient cores.

Changes to KVM include improvements to nested virtualisation (where a VM runs inside another VM) on Intel processors (1, 2, 3 and others). Support for Intel's APIC virtualisation and posted interrupts should reduce overhead when processingPDF interrupts intended for guest systems (1, 2, 3, 4, 5, 6). The new pvpanic driver enables qemu to tell the host when a guest has crashed. A new Hyper-V guest driver enables Windows hosts to instruct Linux guests to quickly get all filesystems into a consistent state to allow the host to create a snapshot of disks used by the guest (host initiated backup).

Performance monitoring

Changes to the perf subsystem include the addition of uretprobes, which allow the kernel to insert breakpoints into the return path for userspace code (1, 2, 3, 4, 5, documentation). This makes it easier for perf to determine when a specific program function was exited. The new perf subcommand 'mem' and corresponding support for 'perf record' and 'perf report' enable memory access profiling on processors with PEBS (precise event based sampling) (1, 2, 3, 4, 5 and others).

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