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Message-ID: <5d9ba064-3288-4926-b9dc-3119bb3404c1@linux.dev>
Date: Wed, 15 Jan 2025 16:03:53 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>
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, horms@...nel.org, bpf@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 13/15] net-timestamp: support tcp_sendmsg for
bpf extension
On 1/12/25 3:37 AM, Jason Xing wrote:
> Introduce tskey_bpf to correlate tcp_sendmsg timestamp with other
> three points (SND/SW/ACK). More details can be found in the
> selftest.
>
> For TCP, tskey_bpf is used to store the initial write_seq value
> the moment tcp_sendmsg is called, so that the last skb of this
> call will have the same tskey_bpf with tcp_sendmsg bpf callback.
>
> UDP works similarly because tskey_bpf can increase by one everytime
> udp_sendmsg gets called. It will be implemented soon.
>
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> ---
> include/linux/skbuff.h | 2 ++
> include/uapi/linux/bpf.h | 3 +++
> net/core/sock.c | 3 ++-
> net/ipv4/tcp.c | 10 ++++++++--
> tools/include/uapi/linux/bpf.h | 3 +++
> 5 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index d3ef8db94a94..3b7b470d5d89 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -609,6 +609,8 @@ struct skb_shared_info {
> };
> unsigned int gso_type;
> u32 tskey;
> + /* For TCP, it records the initial write_seq when sendmsg is called */
> + u32 tskey_bpf;
I would suggest to remove this tskey_bpf addition to skb_shared_info. My
understanding is the intention is to get the delay spent in the
tcp_sendmsg_locked(). I think this can be done in bpf_sk_storage. More below.
>
> /*
> * Warning : all fields before dataref are cleared in __alloc_skb()
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a0aff1b4eb61..87420c0f2235 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7037,6 +7037,9 @@ enum {
> * feature is on. It indicates the
> * recorded timestamp.
> */
> + BPF_SOCK_OPS_TS_TCP_SND_CB, /* Called when every tcp_sendmsg
> + * syscall is triggered
> + */
UDP will need this also?
> };
>
> /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 2f54e60a50d4..e74ab0e2979d 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -958,7 +958,8 @@ void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
> if (sk_is_tcp(sk) && sk_fullsock(sk))
> sock_ops.is_fullsock = 1;
> sock_ops.sk = sk;
> - bpf_skops_init_skb(&sock_ops, skb, 0);
> + if (skb)
> + bpf_skops_init_skb(&sock_ops, skb, 0);
> sock_ops.timestamp_used = 1;
> __cgroup_bpf_run_filter_sock_ops(sk, &sock_ops, CGROUP_SOCK_OPS);
> }
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 0a41006b10d1..b6e0db5e4ead 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -477,7 +477,7 @@ void tcp_init_sock(struct sock *sk)
> }
> EXPORT_SYMBOL(tcp_init_sock);
>
> -static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
> +static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc, u32 first_write_seq)
> {
> struct sk_buff *skb = tcp_write_queue_tail(sk);
> u32 tsflags = sockc->tsflags;
> @@ -500,6 +500,7 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
> tcb->txstamp_ack_bpf = 1;
> shinfo->tx_flags |= SKBTX_BPF;
> shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
Add the bpf prog callout here instead:
bpf_skops_tx_timestamping(sk, skb, BPF_SOCK_OPS_TS_TCP_SND_CB);
If the bpf prog wants to figure out the delay from the very beginning of the
tcp_sendmsg_locked(), a bpf prog (either by tracing the tcp_sendmsg_locked or by
adding a new callout at the beginning of tcp_sendmsg_locked like this patch) can
store a bpf_ktime_get_ns() in the bpf_sk_storage. The bpf prog running here (at
tcp_tx_timestamp) can get that timestamp from the bpf_sk_storage since it has a
hold on the same sk pointer. There is no need to add a new shinfo->tskey_bpf to
measure this part of the delay.
> + shinfo->tskey_bpf = first_write_seq;
> }
> }
>
> @@ -1067,10 +1068,15 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
> int flags, err, copied = 0;
> int mss_now = 0, size_goal, copied_syn = 0;
> int process_backlog = 0;
> + u32 first_write_seq = 0;
> int zc = 0;
> long timeo;
>
> flags = msg->msg_flags;
> + if (SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING)) {
> + first_write_seq = tp->write_seq;
> + bpf_skops_tx_timestamping(sk, NULL, BPF_SOCK_OPS_TS_TCP_SND_CB);
My preference is to skip this bpf callout for now and depends on a bpf trace
program if it is really needed.
> + }
>
> if ((flags & MSG_ZEROCOPY) && size) {
> if (msg->msg_ubuf) {
> @@ -1331,7 +1337,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>
> out:
> if (copied) {
> - tcp_tx_timestamp(sk, &sockc);
> + tcp_tx_timestamp(sk, &sockc, first_write_seq);
> tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
> }
> out_nopush:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 0fe7d663a244..3769e38e052d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7030,6 +7030,9 @@ enum {
> * feature is on. It indicates the
> * recorded timestamp.
> */
> + BPF_SOCK_OPS_TS_TCP_SND_CB, /* Called when every tcp_sendmsg
> + * syscall is triggered
> + */
> };
>
> /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
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