Eric Lee / smarc-ti-linux-kernel

05 Jun, 2014

1 commit

  • c473b2c6f   sh: Replace __get_cpu_var uses ... Browse Code »

    __get_cpu_var() is used for multiple purposes in the kernel source. One
    of them is address calculation via the form &__get_cpu_var(x). This
    calculates the address for the instance of the percpu variable of the
    current processor based on an offset.

    Other use cases are for storing and retrieving data from the current
    processors percpu area. __get_cpu_var() can be used as an lvalue when
    writing data or on the right side of an assignment.

    __get_cpu_var() is defined as :

    #define __get_cpu_var(var) (*this_cpu_ptr(&(var)))

    __get_cpu_var() always only does an address determination. However, store
    and retrieve operations could use a segment prefix (or global register on
    other platforms) to avoid the address calculation.

    this_cpu_write() and this_cpu_read() can directly take an offset into a
    percpu area and use optimized assembly code to read and write per cpu
    variables.

    This patch converts __get_cpu_var into either an explicit address
    calculation using this_cpu_ptr() or into a use of this_cpu operations that
    use the offset. Thereby address calculations are avoided and less
    registers are used when code is generated.

    At the end of the patch set all uses of __get_cpu_var have been removed so
    the macro is removed too.

    The patch set includes passes over all arches as well. Once these
    operations are used throughout then specialized macros can be defined in
    non -x86 arches as well in order to optimize per cpu access by f.e. using
    a global register that may be set to the per cpu base.

    Transformations done to __get_cpu_var()

    1. Determine the address of the percpu instance of the current processor.

    DEFINE_PER_CPU(int, y);
    int *x = &__get_cpu_var(y);

    Converts to

    int *x = this_cpu_ptr(&y);

    2. Same as #1 but this time an array structure is involved.

    DEFINE_PER_CPU(int, y[20]);
    int *x = __get_cpu_var(y);

    Converts to

    int *x = this_cpu_ptr(y);

    3. Retrieve the content of the current processors instance of a per cpu
    variable.

    DEFINE_PER_CPU(int, y);
    int x = __get_cpu_var(y)

    Converts to

    int x = __this_cpu_read(y);

    4. Retrieve the content of a percpu struct

    DEFINE_PER_CPU(struct mystruct, y);
    struct mystruct x = __get_cpu_var(y);

    Converts to

    memcpy(&x, this_cpu_ptr(&y), sizeof(x));

    5. Assignment to a per cpu variable

    DEFINE_PER_CPU(int, y)
    __get_cpu_var(y) = x;

    Converts to

    __this_cpu_write(y, x);

    6. Increment/Decrement etc of a per cpu variable

    DEFINE_PER_CPU(int, y);
    __get_cpu_var(y)++

    Converts to

    __this_cpu_inc(y)

    Signed-off-by: Christoph Lameter
    Tested-by: Geert Uytterhoeven [compilation only]
    Cc: Paul Mundt
    Signed-off-by: Andrew Morton
    Signed-off-by: Linus Torvalds

    Christoph Lameter
     

26 Apr, 2010

1 commit

21 Apr, 2010

1 commit

19 Aug, 2009

1 commit

  • fc6191dd3   sh: Fix up clockevents broadcasting. ... Browse Code »

    This fixes up the clockevents broadcasting code as detailed in commit
    ee348d5a1d810bc9958cabb7c27302aab235d36e ("[ARM] realview: fix broadcast
    tick support"). This saves us from having to do strange ordering things
    with the broadcast clockevent device, relying on the rating instead.

    Signed-off-by: Paul Mundt

    Paul Mundt
     

03 May, 2009

1 commit