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SubjectRe: [PATCH v3 1/5] hw_breakpoint: Add step_needed event attribute
On Mon, Jul 31, 2017 at 04:10:29PM +0530, Pratyush Anand wrote:
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 24a635887f28..7da951f94b47 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -233,6 +233,12 @@ struct hw_perf_event {
> */
> u64 freq_time_stamp;
> u64 freq_count_stamp;
> + /*
> + * A HW breakpoint user can either have it's own step handling
> + * mechanism or it can use default step handling meachanism defined
> + * by arch code. Set step_needed to use default mechanism.
> + */
> + int step_needed;

You'll note that there is an anonymous structure inside the anonymous
union specifically dedicated to hardware breakpoint state. Why not put
it there?

> #endif
> };
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 6c4e523dc1e2..66ce5574e778 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9444,9 +9444,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> } else if (is_write_backward(event)){
> event->overflow_handler = perf_event_output_backward;
> event->overflow_handler_context = NULL;
> + event->hw.step_needed = 1;
> } else {
> event->overflow_handler = perf_event_output_forward;
> event->overflow_handler_context = NULL;
> + event->hw.step_needed = 1;
> }

These here need a comment, because even if I'd know now why the heck we
need that = 1 here, I'd sure as hell won't know tomorrow.

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