Re: [PATCH RFC bpf-next v3 4/6] bpf: report hot simulated callchains when 1M instructions limit is met

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, May 27, 2026 at 12:29:52AM -0700, Eduard Zingerman wrote:

SNIP

> +
>  static int do_check_insn(struct bpf_verifier_env *env, bool *do_print_state)
>  {
>  	int err;
> @@ -17381,6 +17527,7 @@ static int do_check(struct bpf_verifier_env *env)
>  		insn_aux = &env->insn_aux_data[env->insn_idx];
>  
>  		if (++env->insn_processed > BPF_COMPLEXITY_LIMIT_INSNS) {
> +			print_hotspots(env);

hi,
this is really cool feature, I've already used it to fix issues :)

Would it be possible to make this configurable? like to be able
to get this output for program that passed and display more than
3 hottest callchains?

thanks,
jirka


>  			verbose(env,
>  				"BPF program is too large. Processed %d insn\n",
>  				env->insn_processed);
> @@ -17390,6 +17537,12 @@ static int do_check(struct bpf_verifier_env *env)
>  		state->last_insn_idx = env->prev_insn_idx;
>  		state->insn_idx = env->insn_idx;
>  
> +		if (bpf_is_force_checkpoint(env, env->insn_idx) || insn_aux->loop) {
> +			err = update_callchain_profile(env, state);
> +			if (err)
> +				return err;
> +		}
> +
>  		if (bpf_is_prune_point(env, env->insn_idx)) {
>  			err = bpf_is_state_visited(env, env->insn_idx);
>  			if (err < 0)
> @@ -19673,6 +19826,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
>  		return -ENOMEM;
>  
>  	env->bt.env = env;
> +	hash_init(env->callchain_htab);
>  
>  	len = (*prog)->len;
>  	env->insn_aux_data =
> @@ -19945,6 +20099,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
>  	bpf_clear_insn_aux_data(env, 0, env->prog->len);
>  	vfree(env->insn_aux_data);
>  err_free_env:
> +	free_callchain_profile(env);
>  	bpf_stack_liveness_free(env);
>  	kvfree(env->cfg.insn_postorder);
>  	kvfree(env->scc_info);
> 
> -- 
> 2.53.0
>