linux-kernel - Re: [PATCH] sched_ext: Use BTF_ID to resolve task

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Message-ID: <CAADnVQ+gL48HGcs0JyLfq17D-qXyeZEoBJwGgGTO1JcJ3Ykqtw@mail.gmail.com>
Date: Wed, 16 Oct 2024 09:57:07 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tianchen Ding <dtcccc@...ux.alibaba.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>, 
	David Vernet <void@...ifault.com>, Peter Zijlstra <peterz@...radead.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] sched_ext: Use BTF_ID to resolve task_struct

On Tue, Oct 15, 2024 at 7:42 PM Tianchen Ding <dtcccc@...ux.alibaba.com> wrote:
>
> Save the searching time during bpf_scx_init.
>
> Signed-off-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
> ---
>  kernel/sched/ext.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 609b9fb00d6f..1d11a96eefb8 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -5343,7 +5343,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
>
>  extern struct btf *btf_vmlinux;
>  static const struct btf_type *task_struct_type;
> -static u32 task_struct_type_id;
> +BTF_ID_LIST_SINGLE(task_struct_btf_ids, struct, task_struct);
>
>  static bool set_arg_maybe_null(const char *op, int arg_n, int off, int size,
>                                enum bpf_access_type type,
> @@ -5395,7 +5395,7 @@ static bool set_arg_maybe_null(const char *op, int arg_n, int off, int size,
>                  */
>                 info->reg_type = PTR_MAYBE_NULL | PTR_TO_BTF_ID | PTR_TRUSTED;
>                 info->btf = btf_vmlinux;
> -               info->btf_id = task_struct_type_id;
> +               info->btf_id = task_struct_btf_ids[0];
>
>                 return true;
>         }
> @@ -5547,13 +5547,7 @@ static void bpf_scx_unreg(void *kdata, struct bpf_link *link)
>
>  static int bpf_scx_init(struct btf *btf)
>  {
> -       s32 type_id;
> -
> -       type_id = btf_find_by_name_kind(btf, "task_struct", BTF_KIND_STRUCT);
> -       if (type_id < 0)
> -               return -EINVAL;
> -       task_struct_type = btf_type_by_id(btf, type_id);
> -       task_struct_type_id = type_id;
> +       task_struct_type = btf_type_by_id(btf, task_struct_btf_ids[0]);

Good optimization, but it's also unnecessary.

btf_id is already in btf_tracing_ids[BTF_TRACING_TYPE_TASK].