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Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER

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On 10/14/15 5:37 AM, Kaixu Xia wrote:
> +	event->p_sample_disable = &enabler_event->sample_disable;

I don't like it as a concept and it's buggy implementation.
What happens here when enabler is alive, but other event is destroyed?

> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
>   	struct bpf_array *array = container_of(map, struct bpf_array, map);
>   	struct perf_event *event;
>
> -	if (unlikely(index >= array->map.max_entries))
> +	if (unlikely(index > array->map.max_entries))
>   		return -E2BIG;
>
> +	if (index == array->map.max_entries)
> +		index = 0;

what is this hack for ?

Either use notification and user space disable or
call bpf_perf_event_sample_control() manually for each cpu.


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[PATCH V2 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia <xiakaixu@huawei.com> - 2015-10-14 14:40 +0200
  [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER Kaixu Xia <xiakaixu@huawei.com> - 2015-10-14 14:40 +0200
    Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a  new ioctl PERF_EVENT_IOC_SET_ENABLER Alexei Starovoitov <ast@plumgrid.com> - 2015-10-14 23:30 +0200
      Re: [PATCH V2 2/2] bpf: control a set of perf events by creating  a new ioctl PERF_EVENT_IOC_SET_ENABLER xiakaixu <xiakaixu@huawei.com> - 2015-10-15 04:30 +0200

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