On Wed, Oct 16, 2024 at 6:57 PM Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx> wrote:
>
> On 2024/10/17 00:57, Alexei Starovoitov wrote:
> > On Tue, Oct 15, 2024 at 7:42 PM Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx> wrote:
> >>
> >> Save the searching time during bpf_scx_init.
> >>
> >> Signed-off-by: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
> >> ---
> >> 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].
>
> Get it. Thanks!
>
> BTW, do you think we should add a zero check for
> btf_tracing_ids[BTF_TRACING_TYPE_TASK] here?
> task_struct should always be valid. If something wrong, resolve_btfids will also
> throw a warning. I'm not sure whether to add a sanity check here.
Definitely shouldn't add run-time checks.
Build check may work, but feels overkill at this point.
