On Thu, Feb 20, 2025 at 11:15 AM Jason Xing <kerneljasonxing@xxxxxxxxx> wrote:
>
> On Thu, Feb 20, 2025 at 10:55 AM Willem de Bruijn
> <willemdebruijn.kernel@xxxxxxxxx> 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@xxxxxxxxx>
> > > ---
> > > 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 :)
After taking a break, I feel full of energy and I will update them all
as you requested :)
Thanks,
Jason
