Re: [PATCH bpf-next] selftests/bpf: Use PERF_COUNT_HW_CPU_CYCLES event for get_branch_snapshot

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Apr 07, 2023 at 12:01:30PM -0700, Song Liu wrote:
> perf_event with type=PERF_TYPE_RAW and config=0x1b00 turned out to be not
> reliable in ensuring LBR is active. Thus, test_progs:get_branch_snapshot is
> not reliable in some systems. Replace it with PERF_COUNT_HW_CPU_CYCLES
> event, which gives more consistent results.
> 
> Signed-off-by: Song Liu <song@kernel.org>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> index 3948da12a528..0394a1156d99 100644
> --- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> +++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> @@ -37,8 +37,8 @@ static int create_perf_events(void)
>  
>  	/* create perf event */
>  	attr.size = sizeof(attr);
> -	attr.type = PERF_TYPE_RAW;
> -	attr.config = 0x1b00;
> +	attr.type = PERF_TYPE_HARDWARE;
> +	attr.config = PERF_COUNT_HW_CPU_CYCLES;
>  	attr.sample_type = PERF_SAMPLE_BRANCH_STACK;
>  	attr.branch_sample_type = PERF_SAMPLE_BRANCH_KERNEL |
>  		PERF_SAMPLE_BRANCH_USER | PERF_SAMPLE_BRANCH_ANY;
> -- 
> 2.34.1
>