Eric Lee / smarc-fsl-linux-kernel

04 Aug, 2009

1 commit

  • ed8d9adf3   x86, percpu: Add 'percpu_read_stable()' interface for cacheable accesses ... Browse Code »

    This is very useful for some common things like 'get_current()' and
    'get_thread_info()', which can be used multiple times in a function, and
    where the result is cacheable.

    tj: Added the magical undocumented "P" modifier to UP __percpu_arg()
    to force gcc to dereference the pointer value passed in via the
    "p" input constraint. Without this, percpu_read_stable() returns
    the address of the percpu variable. Also added comment explaining
    the difference between percpu_read() and percpu_read_stable().

    Signed-off-by: Linus Torvalds
    Signed-off-by: Tejun Heo
    Signed-off-by: H. Peter Anvin

    Linus Torvalds
     

18 Jan, 2009

1 commit

16 Jan, 2009

1 commit

  • 6dbde3530   percpu: add optimized generic percpu accessors ... Browse Code »

    It is an optimization and a cleanup, and adds the following new
    generic percpu methods:

    percpu_read()
    percpu_write()
    percpu_add()
    percpu_sub()
    percpu_and()
    percpu_or()
    percpu_xor()

    and implements support for them on x86. (other architectures will fall
    back to a default implementation)

    The advantage is that for example to read a local percpu variable,
    instead of this sequence:

    return __get_cpu_var(var);

    ffffffff8102ca2b: 48 8b 14 fd 80 09 74 mov -0x7e8bf680(,%rdi,8),%rdx
    ffffffff8102ca32: 81
    ffffffff8102ca33: 48 c7 c0 d8 59 00 00 mov $0x59d8,%rax
    ffffffff8102ca3a: 48 8b 04 10 mov (%rax,%rdx,1),%rax

    We can get a single instruction by using the optimized variants:

    return percpu_read(var);

    ffffffff8102ca3f: 65 48 8b 05 91 8f fd mov %gs:0x7efd8f91(%rip),%rax

    I also cleaned up the x86-specific APIs and made the x86 code use
    these new generic percpu primitives.

    tj: * fixed generic percpu_sub() definition as Roel Kluin pointed out
    * added percpu_and() for completeness's sake
    * made generic percpu ops atomic against preemption

    Signed-off-by: Ingo Molnar
    Signed-off-by: Tejun Heo

    Ingo Molnar
     

23 Oct, 2008

2 commits