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

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

[Song Liu]

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>
---
 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

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

[Jiri Olsa]

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
> 

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Fri, 7 Apr 2023 12:01:30 -0700 you 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>
> 
> [...]

Here is the summary with links:
  - [bpf-next] selftests/bpf: Use PERF_COUNT_HW_CPU_CYCLES event for get_branch_snapshot
    https://git.kernel.org/bpf/bpf-next/c/3ebf5212bf04

You are awesome, thank you!
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