Eric Lee / smarc-fsl-linux-kernel

24 Feb, 2012

1 commit

  • c5905afb0   static keys: Introduce 'struct static_key', static_key_true()/false() and static… ... Browse Code ยป
    86

    …_key_slow_[inc|dec]()

    So here's a boot tested patch on top of Jason's series that does
    all the cleanups I talked about and turns jump labels into a
    more intuitive to use facility. It should also address the
    various misconceptions and confusions that surround jump labels.

    Typical usage scenarios:

    #include <linux/static_key.h>

    struct static_key key = STATIC_KEY_INIT_TRUE;

    if (static_key_false(&key))
    do unlikely code
    else
    do likely code

    Or:

    if (static_key_true(&key))
    do likely code
    else
    do unlikely code

    The static key is modified via:

    static_key_slow_inc(&key);
    ...
    static_key_slow_dec(&key);

    The 'slow' prefix makes it abundantly clear that this is an
    expensive operation.

    I've updated all in-kernel code to use this everywhere. Note
    that I (intentionally) have not pushed through the rename
    blindly through to the lowest levels: the actual jump-label
    patching arch facility should be named like that, so we want to
    decouple jump labels from the static-key facility a bit.

    On non-jump-label enabled architectures static keys default to
    likely()/unlikely() branches.

    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Acked-by: Jason Baron <jbaron@redhat.com>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Cc: a.p.zijlstra@chello.nl
    Cc: mathieu.desnoyers@efficios.com
    Cc: davem@davemloft.net
    Cc: ddaney.cavm@gmail.com
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
    Signed-off-by: Ingo Molnar <mingo@elte.hu>

    Ingo Molnar