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    Subjectpost-halloween 0.2
    I updated the list of various things that wannabe testers might hit.
    If theres something I missed let me know, and I'll get it right
    next time round..


    The post-halloween document. v0.2
    (aka, 2.5 - what to expect)

    Dave Jones <>

    This document explains some of the new functionality to be found in the 2.5
    Linux kernel, some pitfalls you may encounter, and also points out some new
    features which could really use testing.
    Note, that "contact" below also implies that you should also

    Latest version of this document can always be found at

    (Things not expected to work just yet)
    - The hptraid/promise RAID drivers are currently non functional.
    - Various SCSI drivers still need work, and don't even compile.
    - software suspend is still in development, and in need of more work.
    It is unlikely to work as expected currently.
    - Some filesystems still need work (Coda, Intermezzo).

    Deprecated features:
    - khttpd is gone.
    - Older Direct Rendering Manager (DRM) support (For XFree86 4.0)
    has been removed. Upgrade to XFree86 4.1.0 or higher.

    IO subsystem.
    You should notice considerable throughput improvements over 2.4 due
    to much reworking of the block and the memory management layers.
    Report any regressions in this area to Jens Axboe <>
    and Andrew Morton <>.

    Assorted changes throughout the block layer meant various block
    device drivers had a large scale cleanup whilst being updated to
    newer APIs.

    Kernel preemption.
    The much talked about preemption patches made it into 2.5.
    With this included you should notice much lower latencies especially
    in demanding multimedia applications.
    Note, there are still cases where preemption must be temporarily disabled
    where we do not. If you get "xxx exited with preempt count=n" messages
    in syslog, don't panic, these are non fatal, but are somewhat unclean.
    Report such cases (and any other preemption related problems) to

    O(1) Scheduling improvements.
    Another much talked about feature. Ingo Molnar reworked the process
    scheduler to use an O(1) algorithm. In operation, you should notice
    no changes with low loads, and increased scalability with large numbers
    of processes, especially on large SMP systems. Regressions to

    Input layer
    Possibly the most visible change to the end user. If misconfigured,
    you'll find that your keyboard/mouse/other input device will no longer work.
    2.5 offers a much more flexable interface to devices such as keyboards.
    The downside is more confusing options.
    In the "Input device support" menu, be sure to enable at least the following.

    --- Input I/O drivers
    < > Serial i/o support
    < > i8042 PC Keyboard controller
    [ ] Keyboards
    [ ] Mice

    (Also choose the relevant keyboard/mouse from the list)

    If you find your keyboard/mouse still don't work, edit the file
    drivers/input/serio/i8042.c, and replace the #undef DEBUG
    with a #define DEBUG

    When you boot, you should now see a lot more debugging information.
    Forward this information to Vojtech Pavlik <>

    If you use a KVM switcher, and experience problems, booting
    with the boot time argument 'psmouse_noext' should fix your

    PnP layer
    Support for plug and play devices such as early ISAPNP cards has
    improved a lot in the 2.5 kernel. You should no longer need to
    futz with userspace tools to configure IRQ's and the likes.
    Report any regressions in plug & play functionality to
    Adam Belay <>

    The advanced linux sound architecture got merged into 2.5.
    This offers considerably improved functionality over the
    older OSS drivers, but requires new userspace tools.
    Several distros have shipped ALSA for some time, so you
    may already have the necessary tools. If not, you can find them
    (Note that the OSS drivers are also still functional, and
    still present)

    The 2.5 /proc filesystems exports more statistics, which confuse
    older versions of procps. Rik van Riel and Robert Love have
    been maintaining a forked version of procps during the 2.5 cycle,
    which you can find at

    Framebuffer layer
    James Simmons has reworked the framebuffer/console layer
    considerably during 2.5. Support for some cards is still
    lagging a little, but it should be functionally no different
    than previous incarnations.

    The IDE code was subject to much criticism in early 2.5.x, which
    put off a lot of people from testing. This work was then subsequently
    dropped, and reverted back to a 2.4.18 IDE status.
    (Since then additional work has occured, but not to the extent
    of the first cleanup attempts).
    Additional work on the ATA code is happening in 2.4-ac, and pending
    merging to 2.5

    Tagged command queueing for IDE devices has been included.
    Not all devices may like this, so handle with care.
    If you didn't choose the "TCQ on by default" option,
    you can enable it by using the command

    echo "using_tcq:32" > /proc/ide/hdX/settings
    (replacing 32 with 0 disables TCQ again).
    Report success/failure stories to Jens Axboe <> with
    inclusion of hdparm -i /dev/hdX

    The video4linux API finally got its long awaited cleanup.
    xawtv, bttv and most other existing v4l tools are also compatable
    with the new v4l2 layer. You should notice no loss in functionality.

    Quota reworking
    The new quota system needs new tools.

    CD Recording
    Jens Axboe added the ability to use DMA for writing CDs on
    ATAPI devices. Writing CDs should be much faster than it
    was in 2.4, and also less prone to buffer underruns and the like.
    Updated cdrecord in rpm and tar.gz can be found at

    With the above tools, you also no longer need ide-scsi
    in order to use an IDE CD writer.

    Ripping audio tracks off of CDs now also uses DMA and should
    be notably faster. You can also find an updated cdda2wav
    at the same location.

    Send good/bad reports of audio extraction with cdda2wav
    and burning with cdrecord to Jens Axboe <>

    More info at &

    A number of additional filesystems have made their way into 2.5.
    Whilst these have had testing out of tree, the level of testing
    after merging is unparalleled. Be wary of trusting data to immature
    filesystems. A number of new features and improvements have also
    been made to the existing filesystems from 2.4.

    Reports of stress testing with the various tools available would
    be beneficial.

    Support has been added for NFSv4 (server and client), and additionally,
    NFS over TCP. Reports of interoperability with other OS's would be useful.

    In simple terms, the driverfs filesystem is a saner way for
    drivers to export their innards than /proc.
    This filesystem is always compiled in, and can be mounted
    just like another virtual filesystem. No userspace tools
    beyond cat and echo are needed.

    mount -t driverfs none /sys

    *NB*, at some point the name of this filesystem will be changing to sysfs.
    See Documentation/filesystems/sysfs.txt for more info.

    The SGI XFS filesystem has been merged, and has a number of userspace
    features. Users are encouraged to read
    for more information.
    The various utilties for creating and manipulating XFS volumes can
    be found on SGI's ftp server..

    Support utilities and documentation for the common internet file system (CIFS)
    can be found at

    EXT3 Htree support.
    The ext3 filesystem has gained indexed directory support, which offers
    considerable performance gains when used on filesystems with large directories.
    In order to use the htree feature, you need at least version 1.29 of e2fsprogs.
    Existing filesystems can be converted using the command "tune2fs -O dir_index /dev/hdXXX"
    The latest e2fsprogs can be found at

    A system wide performance profiler has been included in 2.5.
    The userspace utilities for this are very young, and still being developed.
    You can find out more at

    Simple boot flag support.
    The SBF specification is an x86 BIOS extension that allows improved
    system boot speeds. It does this by marking a CMOS field to say
    "I booted okay, skip extensive POST next reboot".
    Userspace tool is at
    More info on SBF is at

    x86 CPU detection.
    The CPU detection code got a pretty hefty shake up. To be certain your
    CPU has all relevant workarounds applied, be sure to check that it was
    detected correctly. cat /proc/cpuinfo will tell what the kernel thinks it is.
    Likewise, the x86 MTRR driver got a considerable makeover.
    Any regressions in both should go to

    Extra tainting.
    Running certain AMD processors in SMP boxes is out of spec, and will taint
    the kernel with the 'S' flag. Running 2 Athlon XPs for example may seem to
    work fine, but may also introduce difficult to pin down bugs.
    In time it's likely this tainting will be extended to cover other out of
    spec cases.

    Power management.
    2.5 contains a more up to date snapshot of the ACPI driver. Should
    you experience any problems booting, try booting with the argument
    "acpi=off" to rule out any ACPI interaction. ACPI has a much more involved
    role in bringing the system up in 2.5 than it did in 2.4
    The old "acpismp=force" boot option is now obsolete, and will be ignored
    due to the old "mini ACPI" parser being removed.

    CPU frequency scaling.
    Certain processors have the facility to scale their voltage/clockspeed.
    2.5 introduces an interface to this feature, see Documentation/cpufreq
    for more information. This functionality also covers features like
    Intel's speedstep, and will be extended in time to cover the Powernow
    feature present in mobile Athlons.

    Background polling of MCE
    The machine check handler has been extended so that it regularly polls
    for any problems on AMD Athlon systems. This may result in machine check
    exceptions occuring more frequently than they did in 2.4 on out of spec
    systems (Overclocking/poor cooling/underated PSU etc..).

    LVM2 - DeviceMapper.
    The LVM code got a massive overhaul (read as: replacement).
    This means new tools are needed to manage the device mapper.
    You can get these from

    Debugging options.
    During the stabilising period, it's likely that the debugging options
    in the kernel hacking menu will trigger quite a few problems.
    Please report any of these problems to
    rather than just disabling the relevant CONFIG_ options.

    - Reiser4 ?
    - ipsec ?
    - ebtables
    - compilers
    When compiled with a modern gcc (Ie gcc 3.x), 2.5 will use additional
    optimisations that 2.4 didn't. This may shake out compiler bugs that
    2.4 didn't expose. The recommended compiler is still 2.95.3.
    - boot time root= parsing changed.
    ramdisks now have ram<n> isntead of rd<n> and cm206 - cm206cd (instead of cm206).

    | Dave Jones.
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