Re: [PATCHv2 bpf-next 22/23] selftests/bpf: Add tracing multi attach benchmark test

[Leon Hwang <leon.hwang@linux.dev>]

On 5/3/26 06:21, Jiri Olsa wrote:
> Adding benchmark test that attaches to (almost) all allowed tracing
> functions and display attach/detach times.
> 
>   # ./test_progs -t tracing_multi_bench_attach -v
>   bpf_testmod.ko is already unloaded.
>   Loading bpf_testmod.ko...
>   Successfully loaded bpf_testmod.ko.
>   serial_test_tracing_multi_bench_attach:PASS:btf__load_vmlinux_btf 0 nsec
>   serial_test_tracing_multi_bench_attach:PASS:tracing_multi_bench__open_and_load 0 nsec
>   serial_test_tracing_multi_bench_attach:PASS:get_syms 0 nsec
>   serial_test_tracing_multi_bench_attach:PASS:bpf_program__attach_tracing_multi 0 nsec
>   serial_test_tracing_multi_bench_attach: found 51186 functions
>   serial_test_tracing_multi_bench_attach: attached in   1.295s
>   serial_test_tracing_multi_bench_attach: detached in   0.243s
>   #507     tracing_multi_bench_attach:OK
>   Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
>   Successfully unloaded bpf_testmod.ko.
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  .../selftests/bpf/prog_tests/tracing_multi.c  | 178 ++++++++++++++++++
>  .../selftests/bpf/progs/tracing_multi_bench.c |  13 ++
>  2 files changed, 191 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_bench.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> index d64d90f4e086..585d6b646d20 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> @@ -9,6 +9,7 @@
>  #include "tracing_multi_intersect.skel.h"
>  #include "tracing_multi_session.skel.h"
>  #include "tracing_multi_fail.skel.h"
> +#include "tracing_multi_bench.skel.h"
>  #include "trace_helpers.h"
>  
>  static __u64 bpf_fentry_test_cookies[] = {
> @@ -543,6 +544,183 @@ static void test_attach_api_fails(void)
>  	tracing_multi_fail__destroy(skel);
>  }
>  
> +/*
> + * Skip several kernel symbols that might not be safe or could cause delays.
> + */
> +static bool skip_symbol(char *name)
> +{
> +	if (!strcmp(name, "arch_cpu_idle"))
> +		return true;
> +	if (!strcmp(name, "default_idle"))
> +		return true;
> +	if (!strncmp(name, "rcu_", 4))
> +		return true;
> +	if (!strcmp(name, "bpf_dispatcher_xdp_func"))
> +		return true;
> +	if (strstr(name, "rcu"))
> +		return true;
> +	if (strstr(name, "trace"))
> +		return true;
> +	if (strstr(name, "irq"))
> +		return true;
> +	if (strstr(name, "bpf_lsm_"))
> +		return true;
> +	if (!strcmp(name, "migrate_enable"))
> +		return true;
> +	if (!strcmp(name, "migrate_disable"))
> +		return true;
> +	if (!strcmp(name, "preempt_count_sub"))
> +		return true;
> +	if (!strcmp(name, "preempt_count_add"))
> +		return true;
> +	return false;
> +}

These names intersect with the list in trace_helpers.c::skip_entry().

It would be better to move this list to trace_helpers.c.

> +
> +#define MAX_BPF_FUNC_ARGS 12
> +
> +static bool btf_type_is_modifier(const struct btf_type *t)
> +{
> +	switch (BTF_INFO_KIND(t->info)) {
> +	case BTF_KIND_TYPEDEF:
> +	case BTF_KIND_VOLATILE:
> +	case BTF_KIND_CONST:
> +	case BTF_KIND_RESTRICT:
> +	case BTF_KIND_TYPE_TAG:
> +		return true;
> +	}
> +	return false;
> +}
> +
> +static bool is_allowed_func(const struct btf *btf, const struct btf_type *t)
> +{
> +	const struct btf_type *proto;
> +	const struct btf_param *args;
> +	__u32 i, nargs;
> +	__s64 ret;
> +
> +	proto = btf_type_by_id(btf, t->type);
> +	if (BTF_INFO_KIND(proto->info) != BTF_KIND_FUNC_PROTO)
> +		return false;
> +
> +	args = (const struct btf_param *)(proto + 1);
> +	nargs = btf_vlen(proto);
> +	if (nargs > MAX_BPF_FUNC_ARGS)
> +		return false;
> +
> +	t = btf__type_by_id(btf, proto->type);
> +	while (t && btf_type_is_modifier(t))
> +		t = btf__type_by_id(btf, t->type);
> +
> +	if (btf_is_struct(t) || btf_is_union(t))
> +		return false;
> +
> +	for (i = 0; i < nargs; i++) {
> +		/* No support for variable args */
> +		if (i == nargs - 1 && args[i].type == 0)
> +			return false;
> +
> +		/* No support of struct argument size greater than 16 bytes */
> +		ret = btf__resolve_size(btf, args[i].type);
> +		if (ret < 0 || ret > 16)
> +			return false;
> +	}
> +
> +	return true;
> +}

NIT: can we avoid copy/pasting the code snippet from libbpf.c?

Thanks,
Leon

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