skb->tstamp was first used as the (rcv) timestamp in real time clock base.
The major usage is to report it to the user (e.g. SO_TIMESTAMP).
Later, skb->tstamp is also set as the (future) delivery_time (e.g. EDT in TCP)
during egress and used by the qdisc (e.g. sch_fq) to make decision on when
the skb can be passed to the dev.
Currently, there is no way to tell skb->tstamp having the (rcv) timestamp
or the delivery_time, so it is always reset to 0 whenever forwarded
between egress and ingress.
While it makes sense to always clear the (rcv) timestamp in skb->tstamp
to avoid confusing sch_fq that expects the delivery_time, it is a
performance issue [0] to clear the delivery_time if the skb finally
egress to a fq@phy-dev.
v3:
- Feedback from v2 is using shinfo(skb)->tx_flags could be racy.
- Considered to reuse a few bits in skb->tstamp to represent
different semantics, other than more code churns, it will break
the bpf usecase which currently can write and then read back
the skb->tstamp.
- Went back to v1 idea on adding a bit to skb and address the
feedbacks on v1:
- Added one bit skb->mono_delivery_time to flag that
the skb->tstamp has the mono delivery_time (EDT), instead
of adding a bit to flag if the skb->tstamp has been forwarded or not.
- Instead of resetting the delivery_time back to the (rcv) timestamp
during recvmsg syscall which may be too late and not useful,
the delivery_time reset in v3 happens earlier once the stack
knows that the skb will be delivered locally.
- Handled the tapping@ingress case by af_packet
- No need to change the (rcv) timestamp to mono clock base as in v1.
The added one bit to flag skb->mono_delivery_time is enough
to keep the EDT delivery_time during forward.
- Added logic to the bpf side to make the existing bpf
running at ingress can still get the (rcv) timestamp
when reading the __sk_buff->tstamp. New __sk_buff->mono_delivery_time
is also added. Test is still needed to test this piece.
Martin KaFai Lau (4):
net: Add skb->mono_delivery_time to distinguish mono delivery_time
from (rcv) timestamp
net: Add skb_clear_tstamp() to keep the mono delivery_time
net: Set skb->mono_delivery_time and clear it when delivering locally
bpf: Add __sk_buff->mono_delivery_time and handle __sk_buff->tstamp
based on tc_at_ingress
drivers/net/loopback.c | 2 +-
include/linux/filter.h | 31 ++++-
include/linux/skbuff.h | 64 ++++++++--
include/uapi/linux/bpf.h | 1 +
net/bridge/br_forward.c | 2 +-
net/bridge/netfilter/nf_conntrack_bridge.c | 5 +-
net/core/dev.c | 4 +-
net/core/filter.c | 140 +++++++++++++++++++--
net/core/skbuff.c | 8 +-
net/ipv4/ip_forward.c | 2 +-
net/ipv4/ip_input.c | 1 +
net/ipv4/ip_output.c | 5 +-
net/ipv4/tcp_output.c | 16 +--
net/ipv6/ip6_input.c | 1 +
net/ipv6/ip6_output.c | 7 +-
net/ipv6/netfilter.c | 5 +-
net/netfilter/ipvs/ip_vs_xmit.c | 6 +-
net/netfilter/nf_dup_netdev.c | 2 +-
net/netfilter/nf_flow_table_ip.c | 4 +-
net/netfilter/nft_fwd_netdev.c | 2 +-
net/openvswitch/vport.c | 2 +-
net/packet/af_packet.c | 4 +-
net/sched/act_bpf.c | 5 +-
net/sched/cls_bpf.c | 6 +-
net/xfrm/xfrm_interface.c | 2 +-
tools/include/uapi/linux/bpf.h | 1 +
26 files changed, 265 insertions(+), 63 deletions(-)
--
2.30.2
