KernelNewbies:

Linux 3.12 [https://lkml.org/lkml/2013/11/3/160 was released on November 2, 2013]

Summary: /!\ /!\ /!\ This page is being written. Sorry for the delay /!\ /!\ /!\

Other news sites that track the changes of this release: LWN [https://lwn.net/Articles/565715/ part 1], [https://lwn.net/Articles/566122/ part 2], [https://lwn.net/Articles/566546/ part 3]

TableOfContents()

1. Prominent features

1.1. Offline data deduplication support in Btrfs

The Btrfs filesystem has gained support for offline data deduplication. Deduplication consists in removing copies of repeated data in the filesystem, since the data is the same only one copy is necessary. In some particular workloads, like virtualization VMs -which often contain similar copies of operating systems- the gains can be enormous. By "offline", it means that the deduplication process is done when the file system is mounted and running, but it's not done automatically and transparently as processes write data, but rather it's triggered by userspace software at a time controlled by the system administrator. Online deduplication will be added future releases.

The bedup deduplication tool has a branch that works against this support. The branch can be found at: https://github.com/g2p/bedup/tree/wip/dedup-syscall

The author of the deduplication support has also written an sample deduplication tool, duperemove, which can be found here: https://github.com/markfasheh/duperemove

Code: [http://git.kernel.org/linus/416161db9b63e353a8fb79d1369779175102fca1 commit]

1.2. Graphic performance boost for AMD Radeon hardware

The website [http://Phoronix.com Phoronix.com] found that graphic performance in modern AMD Radeon GPUs had improved a lot in Linux 3.12. However, there hasn't been any important modification on in the Radeon driver that can cause such massive gains. After [http://www.phoronix.com/scan.php?page=article&item=linux_312_performance&num=1 some investigation], Phoronix found out that the responsible change for this boost wasn't a change in the Radeon driver itself, but [http://anzwix.com/a/Linux%20Kernel/CpufreqOndemandChangeTheCalculationOfTargetFrequ a change to the algorithms in the cpufreq ondemand governor]. Apparently, the ondemand governor was oscillating too much between frequencies, and this oscillation harmed graphic performance for Radeon GPUs. The new algorithm added a better frequency algorithm that eliminates this problem.

Code: [http://git.kernel.org/linus/dfa5bb622555d9da0df21b50f46ebdeef390041b commit]

1.3. Automatic GPU switching in laptops with dual GPUs

Some laptop hardware, like Nvidia Optimus, have two GPUs, one optimized for performance and other for power saving. Until now, some hacks have been needed to switch between these GPUs. In this release, the driver handles the switch automatically

Code: [http://git.kernel.org/linus/0d69704ae348c03bc216b01e32a0e9a2372be419 commit 1], [http://git.kernel.org/linus/5addcf0a5f0fadceba6bd562d0616a1c5d4c1a4d 2], [http://git.kernel.org/linus/246efa4a072f3a2e03010ef0b78b0974ec69c377 3]

1.4. Improved timerless multitasking: allow timekeeping CPU go idle

Linux 3.10 added support for [http://kernelnewbies.org/Linux_3.10#head-62fadba76893e85ee7fb75d548536c5635baca54 timerless multitasking], that is, the ability to run processes without needing to fire up the timer interrupt that is traditionally used to implement multitasking. This support, however, had a caveat: it could turn off interrupts in all CPUs, except one that is used to track timer information for the other CPUs. But that CPU keeps the timer turned on even if all the CPUs are idle, which was useless. This release allows to disable the timer for the timekeeping CPU when all CPUs are idle.

Recommended LWN article: [https://lwn.net/Articles/558284/ Is the whole system idle?]

Code: [http://git.kernel.org/linus/b44379af1cf40050794832c38ea6a64e07eb5087 commit 1], [http://git.kernel.org/linus/8bdf7a252b6398dbd4beaa7a2ba0904cea0abd04 2], [http://git.kernel.org/linus/d4bd54fbac2ea5c30eb976ca557e905f489d55f4 3], [http://git.kernel.org/linus/217af2a2ffbfc1498d1cf3a89fa478b5632df8f7 4], [http://git.kernel.org/linus/0edd1b1784cbdad55aca2c1293be018f53c0ab1d 5], [http://git.kernel.org/linus/eb348b898290da242e46df75ab0b9772003e08b8 6], [http://git.kernel.org/linus/2333210b26cf7aaf48d71343029afb860103d9f9 7], [http://git.kernel.org/linus/eb75767be0e514f97bf1b5cec763696cfc7f7e2a 8]

1.5. RAID5 multithreading

This release attempts to spread the work needed to handle raid 5 stripes to multiple CPUs in the MD ("multiple devices") layer, which allows more IO/sec on fast (SSD) devices.

Code: [http://git.kernel.org/linus/851c30c9badfc6b294c98e887624bff53644ad21 commit1], [http://git.kernel.org/linus/b721420e8719131896b009b11edbbd27d9b85e98 2]

1.6. Improved locking performance for virtualized guests

The operating system that runs in each virtualized guest also runs its own locks. With some locks, like spinning locks, this causes problems when many guests are present and keep spinning and wasting host CPU time and other problems. This release replaces paravirtualized spinlocks with paravirtualized ticket spinlocks, which have better performance properties for virtualized guests and brings speedups on various benchmarks.

Recommended paper: [http://www.xen.org/files/xensummitboston08/LHP.pdf Prevent Guests from Spinning Around]

Code: [http://git.kernel.org/linus/545ac13892ab391049a92108cf59a0d05de7e28c commit 1], [http://git.kernel.org/linus/92b75202e5e8790905f9441ccaea2456cc4621a5 2], [http://git.kernel.org/linus/80bd58fef495d000a02fc5b55ca76d423400e748 3], [http://git.kernel.org/linus/b8fa70b51aa76737bdb6b493901ef7376977489c 4]

1.7. New lockref locking scheme, VFS locking improvements

This release adds a new locking scheme, called "lockref". The "lockref" structure is a combination "spinlock and reference count" that allows optimized reference count accesses. In particular, it guarantees that the reference count will be updated as if the spinlock was held, but using atomic accesses that cover both the reference count and the spinlock words, it can often do the update without actually having to take the lock. This allows to avoid the nastiest cases of spinlock contention on large machines. When updating the reference counts on a large system, it will still end up with the cache line bouncing around, but that's much less noticeable than actually having to spin waiting for the lock. This release already uses lockref to improve the scalability of heavy pathname lookup in large systems.

Recommended LWN article: [https://lwn.net/Articles/565734/ Introducing lockrefs]

Code: [http://git.kernel.org/linus/bc08b449ee14ace4d869adaa1bb35a44ce68d775 commit 1], [http://git.kernel.org/linus/15570086b590a69d59183b08a7770e316cca20a7 2], [http://git.kernel.org/linus/df3d0bbcdb2cafa23a70223d806655bd37e64a9b 3], [http://git.kernel.org/linus/e7d33bb5ea82922e6ddcfc6b28a630b1a4ced071 4], [http://git.kernel.org/linus/232d2d60aa5469bb097f55728f65146bd49c1d25 5], [http://git.kernel.org/linus/71c7356f864dc41e4bd6b884596a422f8954afe0 6]

1.8. Better Out-Of-Memory handling

The Out-Of-Memory state happens when the computer runs out of RAM and swap memory. When Linux gets into this state, it kills a process in order to free memory. This release includes important changes to how the Out-Of-Memory states are handled, the number of out of memory errors sent to userspace and reliability. For more details see the below link.

Recommended LWN article: [https://lwn.net/Articles/562211/#oom Reliable out-of-memory handling]

Code: [http://git.kernel.org/linus/94bce453c78996cc4373d5da6cfabe07fcc6d9f9 commit 1], [http://git.kernel.org/linus/871341023c771ad233620b7a1fb3d9c7031c4e5c 2], [http://git.kernel.org/linus/759496ba6407c6994d6a5ce3a5e74937d7816208 3], [http://git.kernel.org/linus/3a13c4d761b4b979ba8767f42345fed3274991b0 4], [http://git.kernel.org/linus/519e52473ebe9db5cdef44670d5a97f1fd53d721 5], [http://git.kernel.org/linus/fb2a6fc56be66c169f8b80e07ed999ba453a2db2 6], [http://git.kernel.org/linus/3812c8c8f3953921ef18544110dafc3505c1ac62 7]

1.9. DOCUMENT BEING REDACTED RIGHT NOW, MORE FEATURES WILL BE ADDED

2. Drivers and architectures

All the driver and architecture-specific changes can be found in the [http://kernelnewbies.org/Linux_3.12-DriversArch Linux_3.12-DriversArch page]

3. Core

4. Memory management

5. Block layer

6. File systems

7. Networking

8. Crypto

9. Virtualization

10. Security

11. Tracing/perf

KernelNewbies: Linux_3.12 (last edited 2013-11-04 19:44:08 by diegocalleja)