netdev - Re: [PATCH bpf-next v12 10/12] bpf: add BPF_SOCK_OPS_TS_SND

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Message-ID: <CAL+tcoDqqt3QScTHAjWGownjc8-gcMCGq=rYqB9eu=rCwoCLiQ@mail.gmail.com>
Date: Thu, 20 Feb 2025 11:15:36 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, willemb@...gle.com, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev, 
	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 v12 10/12] bpf: add BPF_SOCK_OPS_TS_SND_CB callback

On Thu, Feb 20, 2025 at 10:55 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > This patch introduces a new callback in tcp_tx_timestamp() to correlate
> > tcp_sendmsg timestamp with timestamps from other tx timestamping
> > callbacks (e.g., SND/SW/ACK).
> >
> > Without this patch, BPF program wouldn't know which timestamps belong
> > to which flow because of no socket lock protection. This new callback
> > is inserted in tcp_tx_timestamp() to address this issue because
> > tcp_tx_timestamp() still owns the same socket lock with
> > tcp_sendmsg_locked() in the meanwhile tcp_tx_timestamp() initializes
> > the timestamping related fields for the skb, especially tskey. The
> > tskey is the bridge to do the correlation.
> >
> > For TCP, BPF program hooks the beginning of tcp_sendmsg_locked() and
> > then stores the sendmsg timestamp at the bpf_sk_storage, correlating
> > this timestamp with its tskey that are later used in other sending
> > timestamping callbacks.
> >
> > Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> > ---
> >  include/uapi/linux/bpf.h       | 5 +++++
> >  net/ipv4/tcp.c                 | 4 ++++
> >  tools/include/uapi/linux/bpf.h | 5 +++++
> >  3 files changed, 14 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 9355d617767f..86fca729fbd8 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -7052,6 +7052,11 @@ enum {
> >                                        * when SK_BPF_CB_TX_TIMESTAMPING
> >                                        * feature is on.
> >                                        */
> > +     BPF_SOCK_OPS_TS_SND_CB,         /* Called when every sendmsg syscall
> > +                                      * is triggered. It's used to correlate
> > +                                      * sendmsg timestamp with corresponding
> > +                                      * tskey.
> > +                                      */
> >  };
> >
> >  /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 12b9c4f9c151..4b9739cd3bc5 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -492,6 +492,10 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
> >               if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
> >                       shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
> >       }
> > +
> > +     if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> > +         SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb)
> > +             bpf_skops_tx_timestamping(sk, skb, BPF_SOCK_OPS_TS_SND_CB);
> >  }
> >
> >  static bool tcp_stream_is_readable(struct sock *sk, int target)
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index d3e2988b3b4c..2739ee0154a0 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -7042,6 +7042,11 @@ enum {
> >                                        * when SK_BPF_CB_TX_TIMESTAMPING
> >                                        * feature is on.
> >                                        */
> > +     BPF_SOCK_OPS_TS_SND_CB,         /* Called when every sendmsg syscall
> > +                                      * is triggered. It's used to correlate
> > +                                      * sendmsg timestamp with corresponding
> > +                                      * tskey.
> > +                                      */
>
> Feel free to decline this late in the review process, but a bit more
> bikeshedding..
>
> Can we spell out TSTAMP instead of TS in these definitions? Within
> the context of this series it is self-explanatory, but when reading
> kernel code the meaning of a two letter acronym is not that clear.

Even though I feel reluctant to change across the whole series because
if so, I will adjust in many places. Of course, you're right about the
new name being clearer :)

>
> And instead of SND can we use SENDMSG or something like that?
> SND here confused me as the software timestamp is SCM_TSTAMP_SND.

I'm not sure about this. For TCP, it's not implemented in the
tcp_sendmsg_locked but tcp_tx_timestamp. Well, I have no strong
preference.

You can make the final call :)

Thanks,
Jason

>
> For instance:
>
>     BPF_SOCK_OPS_TSTAMP_SENDMSG_CB,
>     BPF_SOCK_OPS_TSTAMP_SCHED_CB,
>     BPF_SOCK_OPS_TSTAMP_SND_SW_CB,
>     BPF_SOCK_OPS_TSTAMP_SND_HW_CB,
>    (BPF_SOCK_OPS_TSTAMP_TX_COMPLETION_CB,)
>     BPF_SOCK_OPS_TSTAMP_ACK_CB,
>
> (not sure what the OPT in OPT_CB added).
>
>