v2 changes:
- Split out the preload operation to a separate routine from
tcp_sendmsg_locked() and restrict from looping over the supplied
iovec
------
Support write to a listen TCP socket, for immediate
transmission on all later passive connection establishments
parented by the listen socket.
On a normal connection transmission of the data is triggered by the receipt
of the 3rd-ack. On a fastopen (with accepted cookie) connection the data
is sent in the synack packet.
The data preload is done using a sendmsg with a newly-defined flag
(MSG_PRELOAD); the amount of data limited to a single linear sk_buff.
Note that this definition is the last-but-two bit available if "int"
is 32 bits.
Intent: lower latency for server-first protocols using TCP.
Known cases of this use are SMTP and MySQL.
Measurements:
Packet capture (laptop, loopback, TFO requeste) for initial SYN to first
client data packet (5 samples):
- baseline TFO-C 1064 1470 1455 1547 1595 usec
- patched non-TFO 140 150 159 144 153 usec
- patched TFO-C 142 149 149 125 125 usec
Out of scope:
- Client-first protocols
- TLS-on-connect
Testing:
A) packetdrill scripts for
- normal non-TFO
- normal TFO
- synack lost
- 3rd-ack acks only the SYN
- 3rd-ack acks partial data
(NB: packetdrill can only check the data size, not actual content)
B) Application use, running the application testsuite
and manual check of specific cases via packet capture
C) Daily-driver laptop use (not expected to trigger the feature;
only regression-test)
D) KASAN/syzkaller
- enable_syscalls "socket$inet_tcp", "listen", "sendmsg", "accept",
"read", "write", "close", "syz_emit_ethernet", "syz_extract_tcp_res"
- the coverage seems rather limited; the sendmsg onto a listen socket
is there, but I am not convinced actual TCP connections are being
excercised. tcp_minisocks.c is entirely uncovered.
- A need for limiting iteration in the above sendmesg was found (RCU
timeouts), hence v2, but no hint of locking problems.
Eric: could you expand on your previous comment? If it referred to
the listening socket, tcp_sendmsg_locked() is called with the sk
locked.
Jeremy Harris (6):
tcp: support writing to a socket in listening state
tcp: copy write-data from listen socket to accept child socket
tcp: fastopen: add write-data to fastopen synack packet
tcp: transmit any pending data on receipt of 3rd-ack
tcp: fastopen: retransmit data when only the SYN of a synack-with-data
is acked
tcp: fastopen: extend retransmit-queue trimming to handle linear
sk_buff
include/linux/socket.h | 1 +
net/ipv4/tcp.c | 115 ++++++++++++++++++
net/ipv4/tcp_fastopen.c | 3 +-
net/ipv4/tcp_input.c | 15 ++-
net/ipv4/tcp_ipv4.c | 4 +-
net/ipv4/tcp_minisocks.c | 58 ++++++++-
net/ipv4/tcp_output.c | 50 +++++++-
.../perf/trace/beauty/include/linux/socket.h | 1 +
tools/perf/trace/beauty/msg_flags.c | 3 +
9 files changed, 237 insertions(+), 13 deletions(-)
base-commit: f685204c57e87d2a88b159c7525426d70ee745c9
--
2.49.0
