linux-kernel - Re: [PATCH bpf-next v2] bpf: make update_prog_stats always

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Message-ID: <CAADnVQLz7-tVmJ7C3VdNDcL8y07Vyg5Ad+DhKAQ7odQAo_BO=Q@mail.gmail.com>
Date: Mon, 23 Jun 2025 09:26:42 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Menglong Dong <dongml2@...natelecom.cn>
Subject: Re: [PATCH bpf-next v2] bpf: make update_prog_stats always_inline

On Fri, Jun 20, 2025 at 9:57 PM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> The function update_prog_stats() will be called in the bpf trampoline.
> In most cases, it will be optimized by the compiler by making it inline.
> However, we can't rely on the compiler all the time, and just make it
> __always_inline to reduce the possible overhead.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v2:
> - split out __update_prog_stats() and make update_prog_stats()
>   __always_inline, as Alexei's advice
> ---
>  kernel/bpf/trampoline.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index c4b1a98ff726..1f92246117eb 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -911,18 +911,16 @@ static u64 notrace __bpf_prog_enter_recur(struct bpf_prog *prog, struct bpf_tram
>         return bpf_prog_start_time();
>  }
>
> -static void notrace update_prog_stats(struct bpf_prog *prog,
> -                                     u64 start)
> +static void notrace __update_prog_stats(struct bpf_prog *prog, u64 start)
>  {
>         struct bpf_prog_stats *stats;
>
> -       if (static_branch_unlikely(&bpf_stats_enabled_key) &&
> -           /* static_key could be enabled in __bpf_prog_enter*
> -            * and disabled in __bpf_prog_exit*.
> -            * And vice versa.
> -            * Hence check that 'start' is valid.
> -            */
> -           start > NO_START_TIME) {
> +       /* static_key could be enabled in __bpf_prog_enter*
> +        * and disabled in __bpf_prog_exit*.
> +        * And vice versa.
> +        * Hence check that 'start' is valid.
> +        */


Instead of old networking style I reformatted above to normal
kernel style comment.

> +       if (start > NO_START_TIME) {

and refactored it to <= and removed extra indent in below.
while applying.