netdev - Re: [PATCH bpf-next v10 11/12] bpf: support selective sampling for bpf timestamping

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Message-ID: <CAL+tcoBJ0JEKBZUf-vzPCdkAXPb+PEB8FBYb5T6AoV3Hy-vjiA@mail.gmail.com>
Date: Thu, 13 Feb 2025 15:26:55 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, willemdebruijn.kernel@...il.com, 
	willemb@...gle.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, shuah@...nel.org, ykolal@...com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v10 11/12] bpf: support selective sampling for
 bpf timestamping

On Thu, Feb 13, 2025 at 7:49 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> On 2/11/25 10:18 PM, Jason Xing wrote:
> > Add the bpf_sock_ops_enable_tx_tstamp kfunc to allow BPF programs to
> > selectively enable TX timestamping on a skb during tcp_sendmsg().
> >
> > For example, BPF program will limit tracking X numbers of packets
> > and then will stop there instead of tracing all the sendmsgs of
> > matched flow all along. It would be helpful for users who cannot
> > afford to calculate latencies from every sendmsg call probably
> > due to the performance or storage space consideration.
> >
> > Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> > ---
> >   kernel/bpf/btf.c  |  1 +
> >   net/core/filter.c | 32 +++++++++++++++++++++++++++++++-
> >   2 files changed, 32 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 9433b6467bbe..740210f883dc 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -8522,6 +8522,7 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
> >       case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
> >       case BPF_PROG_TYPE_CGROUP_SOCKOPT:
> >       case BPF_PROG_TYPE_CGROUP_SYSCTL:
> > +     case BPF_PROG_TYPE_SOCK_OPS:
> >               return BTF_KFUNC_HOOK_CGROUP;
> >       case BPF_PROG_TYPE_SCHED_ACT:
> >               return BTF_KFUNC_HOOK_SCHED_ACT;
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 7f56d0bbeb00..36793c68b125 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -12102,6 +12102,26 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
> >   #endif
> >   }
> >
> > +__bpf_kfunc int bpf_sock_ops_enable_tx_tstamp(struct bpf_sock_ops_kern *skops,
> > +                                           u64 flags)
> > +{
> > +     struct sk_buff *skb;
> > +     struct sock *sk;
> > +
> > +     if (skops->op != BPF_SOCK_OPS_TS_SND_CB)
> > +             return -EOPNOTSUPP;
>
> It still needs to test the "flags" such that it can be used in the future....
>
>         if (flags)
>                 return -EINVAL;

Will add it.

> > +
> > +     skb = skops->skb;
> > +     sk = skops->sk;
> > +     skb_shinfo(skb)->tx_flags |= SKBTX_BPF;
> > +     if (sk_is_tcp(sk)) {
>
> Unnecessary check like this will only confuse reader. Remove it and revisit when
> UDP will be supported.

Okay.

Thanks,
Jason

>
> > +             TCP_SKB_CB(skb)->txstamp_ack |= TSTAMP_ACK_BPF;
> > +             skb_shinfo(skb)->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> >   __bpf_kfunc_end_defs();
> >
> >   int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
> > @@ -12135,6 +12155,10 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_tcp_reqsk)
> >   BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS)
> >   BTF_KFUNCS_END(bpf_kfunc_check_set_tcp_reqsk)
> >
> > +BTF_KFUNCS_START(bpf_kfunc_check_set_sock_ops)
> > +BTF_ID_FLAGS(func, bpf_sock_ops_enable_tx_tstamp, KF_TRUSTED_ARGS)
> > +BTF_KFUNCS_END(bpf_kfunc_check_set_sock_ops)
> > +
> >   static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
> >       .owner = THIS_MODULE,
> >       .set = &bpf_kfunc_check_set_skb,
> > @@ -12155,6 +12179,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_tcp_reqsk = {
> >       .set = &bpf_kfunc_check_set_tcp_reqsk,
> >   };
> >
> > +static const struct btf_kfunc_id_set bpf_kfunc_set_sock_ops = {
> > +     .owner = THIS_MODULE,
> > +     .set = &bpf_kfunc_check_set_sock_ops,
> > +};
> > +
> >   static int __init bpf_kfunc_init(void)
> >   {
> >       int ret;
> > @@ -12173,7 +12202,8 @@ static int __init bpf_kfunc_init(void)
> >       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
> >       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
> >                                              &bpf_kfunc_set_sock_addr);
> > -     return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk);
> > +     ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk);
> > +     return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SOCK_OPS, &bpf_kfunc_set_sock_ops);
> >   }
> >   late_initcall(bpf_kfunc_init);
> >
>