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    Subject[PATCH 2/5] perf core: Set event's default overflow_handler
    Date
    Set a default event->overflow_handler in perf_event_alloc() so don't
    need checking event->overflow_handler in __perf_event_overflow().
    Following commits can give a different default overflow_handler.

    No extra performance introduced into hot path because in the original
    code we still need reading this handler from memory. A conditional branch
    is avoided so actually we remove some instructions.

    Initial idea comes from Peter at [1].

    [1] http://lkml.kernel.org/r/20130708121557.GA17211@twins.programming.kicks-ass.net

    Signed-off-by: Wang Nan <wangnan0@huawei.com>
    Cc: He Kuang <hekuang@huawei.com>
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Zefan Li <lizefan@huawei.com>
    Cc: pi3orama@163.com
    ---
    kernel/events/core.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 9e9c84da..f79c4be 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -6402,10 +6402,7 @@ static int __perf_event_overflow(struct perf_event *event,
    irq_work_queue(&event->pending);
    }

    - if (event->overflow_handler)
    - event->overflow_handler(event, data, regs);
    - else
    - perf_event_output(event, data, regs);
    + event->overflow_handler(event, data, regs);

    if (*perf_event_fasync(event) && event->pending_kill) {
    event->pending_wakeup = 1;
    @@ -7874,8 +7871,13 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
    context = parent_event->overflow_handler_context;
    }

    - event->overflow_handler = overflow_handler;
    - event->overflow_handler_context = context;
    + if (overflow_handler) {
    + event->overflow_handler = overflow_handler;
    + event->overflow_handler_context = context;
    + } else {
    + event->overflow_handler = perf_event_output;
    + event->overflow_handler_context = NULL;
    + }

    perf_event__state_init(event);

    --
    1.8.3.4
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