Eric Lee / smarc-fsl-linux-kernel

05 Oct, 2006

1 commit

  • 7d12e780e   IRQ: Maintain regs pointer globally rather than passing to IRQ handlers ... Browse Code »

    Maintain a per-CPU global "struct pt_regs *" variable which can be used instead
    of passing regs around manually through all ~1800 interrupt handlers in the
    Linux kernel.

    The regs pointer is used in few places, but it potentially costs both stack
    space and code to pass it around. On the FRV arch, removing the regs parameter
    from all the genirq function results in a 20% speed up of the IRQ exit path
    (ie: from leaving timer_interrupt() to leaving do_IRQ()).

    Where appropriate, an arch may override the generic storage facility and do
    something different with the variable. On FRV, for instance, the address is
    maintained in GR28 at all times inside the kernel as part of general exception
    handling.

    Having looked over the code, it appears that the parameter may be handed down
    through up to twenty or so layers of functions. Consider a USB character
    device attached to a USB hub, attached to a USB controller that posts its
    interrupts through a cascaded auxiliary interrupt controller. A character
    device driver may want to pass regs to the sysrq handler through the input
    layer which adds another few layers of parameter passing.

    I've build this code with allyesconfig for x86_64 and i386. I've runtested the
    main part of the code on FRV and i386, though I can't test most of the drivers.
    I've also done partial conversion for powerpc and MIPS - these at least compile
    with minimal configurations.

    This will affect all archs. Mostly the changes should be relatively easy.
    Take do_IRQ(), store the regs pointer at the beginning, saving the old one:

    struct pt_regs *old_regs = set_irq_regs(regs);

    And put the old one back at the end:

    set_irq_regs(old_regs);

    Don't pass regs through to generic_handle_irq() or __do_IRQ().

    In timer_interrupt(), this sort of change will be necessary:

    - update_process_times(user_mode(regs));
    - profile_tick(CPU_PROFILING, regs);
    + update_process_times(user_mode(get_irq_regs()));
    + profile_tick(CPU_PROFILING);

    I'd like to move update_process_times()'s use of get_irq_regs() into itself,
    except that i386, alone of the archs, uses something other than user_mode().

    Some notes on the interrupt handling in the drivers:

    (*) input_dev() is now gone entirely. The regs pointer is no longer stored in
    the input_dev struct.

    (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking. It does
    something different depending on whether it's been supplied with a regs
    pointer or not.

    (*) Various IRQ handler function pointers have been moved to type
    irq_handler_t.

    Signed-Off-By: David Howells
    (cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)

    David Howells
     

11 Jan, 2006

1 commit

  • 33f0f88f1   [PATCH] TTY layer buffering revamp ... Browse Code »

    The API and code have been through various bits of initial review by
    serial driver people but they definitely need to live somewhere for a
    while so the unconverted drivers can get knocked into shape, existing
    drivers that have been updated can be better tuned and bugs whacked out.

    This replaces the tty flip buffers with kmalloc objects in rings. In the
    normal situation for an IRQ driven serial port at typical speeds the
    behaviour is pretty much the same, two buffers end up allocated and the
    kernel cycles between them as before.

    When there are delays or at high speed we now behave far better as the
    buffer pool can grow a bit rather than lose characters. This also means
    that we can operate at higher speeds reliably.

    For drivers that receive characters in blocks (DMA based, USB and
    especially virtualisation) the layer allows a lot of driver specific
    code that works around the tty layer with private secondary queues to be
    removed. The IBM folks need this sort of layer, the smart serial port
    people do, the virtualisers do (because a virtualised tty typically
    operates at infinite speed rather than emulating 9600 baud).

    Finally many drivers had invalid and unsafe attempts to avoid buffer
    overflows by directly invoking tty methods extracted out of the innards
    of work queue structs. These are no longer needed and all go away. That
    fixes various random hangs with serial ports on overflow.

    The other change in here is to optimise the receive_room path that is
    used by some callers. It turns out that only one ldisc uses receive room
    except asa constant and it updates it far far less than the value is
    read. We thus make it a variable not a function call.

    I expect the code to contain bugs due to the size alone but I'll be
    watching and squashing them and feeding out new patches as it goes.

    Because the buffers now dynamically expand you should only run out of
    buffering when the kernel runs out of memory for real. That means a lot of
    the horrible hacks high performance drivers used to do just aren't needed any
    more.

    Description:

    tty_insert_flip_char is an old API and continues to work as before, as does
    tty_flip_buffer_push() [this is why many drivers dont need modification]. It
    does now also return the number of chars inserted

    There are also

    tty_buffer_request_room(tty, len)

    which asks for a buffer block of the length requested and returns the space
    found. This improves efficiency with hardware that knows how much to
    transfer.

    and tty_insert_flip_string_flags(tty, str, flags, len)

    to insert a string of characters and flags

    For a smart interface the usual code is

    len = tty_request_buffer_room(tty, amount_hardware_says);
    tty_insert_flip_string(tty, buffer_from_card, len);

    More description!

    At the moment tty buffers are attached directly to the tty. This is causing a
    lot of the problems related to tty layer locking, also problems at high speed
    and also with bursty data (such as occurs in virtualised environments)

    I'm working on ripping out the flip buffers and replacing them with a pool of
    dynamically allocated buffers. This allows both for old style "byte I/O"
    devices and also helps virtualisation and smart devices where large blocks of
    data suddenely materialise and need storing.

    So far so good. Lots of drivers reference tty->flip.*. Several of them also
    call directly and unsafely into function pointers it provides. This will all
    break. Most drivers can use tty_insert_flip_char which can be kept as an API
    but others need more.

    At the moment I've added the following interfaces, if people think more will
    be needed now is a good time to say

    int tty_buffer_request_room(tty, size)

    Try and ensure at least size bytes are available, returns actual room (may be
    zero). At the moment it just uses the flipbuf space but that will change.
    Repeated calls without characters being added are not cumulative. (ie if you
    call it with 1, 1, 1, and then 4 you'll have four characters of space. The
    other functions will also try and grow buffers in future but this will be a
    more efficient way when you know block sizes.

    int tty_insert_flip_char(tty, ch, flag)

    As before insert a character if there is room. Now returns 1 for success, 0
    for failure.

    int tty_insert_flip_string(tty, str, len)

    Insert a block of non error characters. Returns the number inserted.

    int tty_prepare_flip_string(tty, strptr, len)

    Adjust the buffer to allow len characters to be added. Returns a buffer
    pointer in strptr and the length available. This allows for hardware that
    needs to use functions like insl or mencpy_fromio.

    Signed-off-by: Alan Cox
    Cc: Paul Fulghum
    Signed-off-by: Hirokazu Takata
    Signed-off-by: Serge Hallyn
    Signed-off-by: Jeff Dike
    Signed-off-by: John Hawkes
    Signed-off-by: Martin Schwidefsky
    Signed-off-by: Adrian Bunk
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    Alan Cox
     

08 Sep, 2005

1 commit

24 Jun, 2005

1 commit

17 May, 2005

1 commit

  • 1ff2c873c   [PATCH] serport oops fix ... Browse Code »

    serport - avoid calling serio_interrupt or serio_write_wakeup on unregistered
    port. Also fix memory leak which could happen if serport was left unused by
    moving serio allocation down to serport_ldisc_read.

    Signed-off-by: Dmitry Torokhov
    Cc: Vojtech Pavlik
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    Dmitry Torokhov
     

17 Apr, 2005

1 commit

  • 1da177e4c   Linux-2.6.12-rc2 ... Browse Code »

    Initial git repository build. I'm not bothering with the full history,
    even though we have it. We can create a separate "historical" git
    archive of that later if we want to, and in the meantime it's about
    3.2GB when imported into git - space that would just make the early
    git days unnecessarily complicated, when we don't have a lot of good
    infrastructure for it.

    Let it rip!

    Linus Torvalds