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Faster boot

Following on from the improvements to boot time in Fedora 10, the programming team has continued to fight the good fight in this area in version 11, with the talk now being of a "20 second startup". On our newish test system, with a G45 chip-set on an Intel motherboard, a Core 2 Duo E6750 and a modern SATA-2 hard drive, 22 seconds elapsed, rather than the advertised 20, from first seeing the GRUB boot manager to the login screen.

This makes the new version of Fedora around four seconds faster than its predecessor, but still nearly four seconds slower than Ubuntu 9.04. Like Fedora 10, however, Ubuntu 9.04 initially takes rather more than 30 seconds to boot, as the Ubuntu kernel has problems with USB initialisation not shared by Fedora 11. Only after deactivating legacy support in the BIOS do both Ubuntu 9.04 and Fedora 10 get properly up to speed.

Ext4

The last few versions of Fedora could be installed on an Ext4 file system by using undocumented boot parameters; Fedora 11 goes one better and uses Ext4 as its default file system. To protect users from the much discussed risk of data loss in the event of a crash when using Ext4, the Fedora development team have incorporated some of the changes planned for Linux 2.6.30 into their kernel, changes which significantly reduce the risk of data loss as a result of delayed allocation. GRUB still does not offer Ext4 support under Fedora, however, with the result that users will need to set up a separate boot partition.

Ext4 is the only option when installing Fedora using a LiveCD, but Ext3 is still available as an option when installing from the full downloaded CD or DVD ISO image. More adventurous users can install Fedora 11 on the still experimental Btrfs file system – seen by some Linux file system developers as the chosen 'next generation file system' – using the 'icantbelieveitsnotbtr' parameter when booting. However, this is intended testers and developers only.

The core issues

Fedora 11 is available for 32 (i386) and 64-bit (x86_64) x86 CPUs from AMD and Intel. There is also a PowerPC version (ppc). The 32-bit version can also be installed on 64-bit CPUs, here however, it does require PAE support in order to address more than 4 GB of RAM.

It was originally intended that, on x86-64 processors, the 32-bit version of Fedora 11 (i386) would configure an x86-64 kernel together with a 32-bit userland environment. In the event time constraints have led to this idea being dropped. In contrast to previous versions, the Fedora 11 installer installs a 32-bit kernel with PAE support (CONFIG_X86_PAE=y) on processors with NoExecute (NX) support, in order to take advantage of AMD's Enhanced Virus Protection/EVP and Intel's Execute Disable memory protection technologies. This is offered by almost all CPUs sold within the last two to three years, but with a 32-bit kernel can only be addressed via PAE – in this respect it is no different to Windows, which has long configured a PAE kernel to utilise NX on modern systems.

Fedora's PAE kernel also addresses up to 64 GB of RAM (CONFIG_HIGHMEM64G=y), which on 32-bit x86 systems can only occur with the aid of PAE. Kernels with support for up to 64 GB of RAM are in some cases significantly slower in some microbenchmarks than 64-bit kernels. In a recent email on the Linux Kernel Mailing List (LKML), Linus Torvalds stated that "it's one of those options that we do to support crazy hardware, and it is EXTREMELY expensive ([...] HIGHMEM64G is always expensive for forks, but nobody sane ever enables it)".

In the vast majority of cases, this overhead is likely to be negligible and to have no discernible effect. Where it does, users can switch to a kernel compiled for i586 CPUs, which Fedora configures on processors which do not have NX support. Fedora doesn't offer an i686 kernel without PAE support. Because the package with the PAE kernel carries the suffix "PAE", this also has to be used elsewhere – the package containing the files required to compile a kernel module suitable for the PAE kernel is thus called "kernel-PAE-devel".

Self-limiting

Fedora omits various drivers which are not in the main Linux development tree, but are included in many other distributions, such as em8300, kqemu and ndiswrapper, and Linux staging drivers such as rt2860 and rt2870. This is aimed at making it easier to update to later kernel versions, which Fedora often releases in the form of regular updates. As the Fedora developers never tire of stressing, if these drivers aren't good enough for kernel developers, what makes them good enough for Fedora?

As a result, hardware support in some areas is not as comprehensive as in the recently released Linux 2.6.28-based Ubuntu 9.04. Some of the more common drivers omitted from Fedora can be added using add-on package repositories such as RPM Fusion; see "The usually unavoidable extensions" at the end of this article for details. Hardware support tends to improve substantially with time, however, as a result of the updates to new kernel versions mentioned above, and the numerous improvements and new and improved drivers these updates involve. As a result Fedora users are retrospectively supplied with hardware drivers which are currently still weeks or months from release. This is not the case with most other mainstream distributions, where users usually have to wait for the next distribution or use a development version.

Next: Substructure and the latest software

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