Re: [PATCH net-next 5/6] bpf: enable bpf timestamping rx in TCP layer

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 18/05/2026 10.23, Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent.com>
> 
> Add two if statements to accurately isolate bpf timestamping and so
> timestamping. They can work respectively.
> 
> As to so_timestamping, only add a loose condition via report flags
> to avoid duplicate strict checks that is done in tcp_recv_timestamp()
> and performance impact. If the loose condition is hit,
> tcp_recv_timestamp() is able to handle the exact case and doesn't
> hamper the existing timestamping feature.
> 
> Make it work in TCP protocol.
> 
> Signed-off-by: Jason Xing <kernelxing@tencent.com>
> ---
>   net/ipv4/tcp.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 21ece4c71612..64c69bb3578a 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2949,8 +2949,18 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int flags)
>   	release_sock(sk);
>   
>   	if ((cmsg_flags | msg->msg_get_inq) && ret >= 0) {
> -		if (cmsg_flags & TCP_CMSG_TS)
> -			tcp_recv_timestamp(msg, sk, &tss);
> +		if (cmsg_flags & TCP_CMSG_TS) {
> +			u32 tsflags = READ_ONCE(sk->sk_tsflags);
> +
> +			if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> +			    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_RX_TIMESTAMPING))
> +				bpf_skops_rx_timestamping(sk, &tss,
> +							  BPF_SOCK_OPS_TSTAMP_RCV_CB);

Does this mean I can enable timestamp reading per cgroup?

In Simon's netstacklat[1] tool we are forced process all RX timestamp
(hooking fentry/tcp_recv_timestamp), and then we have a BPF filter[2] on
the cgroup IDs that we are interested in (which is a significant
overhead, as this is deployed at Cloudflare production scale).


[1] https://github.com/xdp-project/bpf-examples/tree/main/netstacklat

[2] 
https://github.com/xdp-project/bpf-examples/blob/main/netstacklat/netstacklat.bpf.c#L484-L488


> +			if (sock_flag(sk, SOCK_RCVTSTAMP) ||
> +			    tsflags & SOF_TIMESTAMPING_SOFTWARE ||
> +			    tsflags & SOF_TIMESTAMPING_RAW_HARDWARE)
> +				tcp_recv_timestamp(msg, sk, &tss);
> +		}
>   		if ((cmsg_flags & TCP_CMSG_INQ) | msg->msg_get_inq) {
>   			msg->msg_inq = tcp_inq_hint(sk);
>   			if (cmsg_flags & TCP_CMSG_INQ)