Stefano, As soon as I get your "Reviewed-by" on this I will send it to netdev. ///jon On 2024-02-08 09:50, Jon Maloy wrote:

When reading received messages from a socket with MSG_PEEK, we may want to read the contents with an offset, like we can do with pread/preadv() when reading files. Currently, it is not possible to do that.

In this commit, we add support for the SO_PEEK_OFF socket option for TCP, in a similar way it is done for Unix Domain sockets.

In the iperf3 log examples shown below, we can observe a throughput improvement of 15-20 % in the direction host->namespace when using the protocol splicer 'pasta' (https://passt.top). This is a consistent result.

pasta(1) and passt(1) implement user-mode networking for network namespaces (containers) and virtual machines by means of a translation layer between Layer-2 network interface and native Layer-4 sockets (TCP, UDP, ICMP/ICMPv6 echo).

Received, pending TCP data to the container/guest is kept in kernel buffers until acknowledged, so the tool routinely needs to fetch new data from socket, skipping data that was already sent.

At the moment this is implemented using a dummy buffer passed to recvmsg(). With this change, we don't need a dummy buffer and the related buffer copy (copy_to_user()) anymore.

passt and pasta are supported in KubeVirt and libvirt/qemu.

jmaloy@freyr:~/passt$ perf record -g ./pasta --config-net -f SO_PEEK_OFF not supported by kernel.

jmaloy@freyr:~/passt# iperf3 -s ----------------------------------------------------------- Server listening on 5201 (test #1) ----------------------------------------------------------- Accepted connection from 192.168.122.1, port 44822 [ 5] local 192.168.122.180 port 5201 connected to 192.168.122.1 port 44832 [ ID] Interval Transfer Bitrate [ 5] 0.00-1.00 sec 1.02 GBytes 8.78 Gbits/sec [ 5] 1.00-2.00 sec 1.06 GBytes 9.08 Gbits/sec [ 5] 2.00-3.00 sec 1.07 GBytes 9.15 Gbits/sec [ 5] 3.00-4.00 sec 1.10 GBytes 9.46 Gbits/sec [ 5] 4.00-5.00 sec 1.03 GBytes 8.85 Gbits/sec [ 5] 5.00-6.00 sec 1.10 GBytes 9.44 Gbits/sec [ 5] 6.00-7.00 sec 1.11 GBytes 9.56 Gbits/sec [ 5] 7.00-8.00 sec 1.07 GBytes 9.20 Gbits/sec [ 5] 8.00-9.00 sec 667 MBytes 5.59 Gbits/sec [ 5] 9.00-10.00 sec 1.03 GBytes 8.83 Gbits/sec [ 5] 10.00-10.04 sec 30.1 MBytes 6.36 Gbits/sec - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate [ 5] 0.00-10.04 sec 10.3 GBytes 8.78 Gbits/sec receiver ----------------------------------------------------------- Server listening on 5201 (test #2) ----------------------------------------------------------- ^Ciperf3: interrupt - the server has terminated jmaloy@freyr:~/passt# logout [ perf record: Woken up 23 times to write data ] [ perf record: Captured and wrote 5.696 MB perf.data (35580 samples) ] jmaloy@freyr:~/passt$

jmaloy@freyr:~/passt$ perf record -g ./pasta --config-net -f SO_PEEK_OFF supported by kernel.

jmaloy@freyr:~/passt# iperf3 -s ----------------------------------------------------------- Server listening on 5201 (test #1) ----------------------------------------------------------- Accepted connection from 192.168.122.1, port 52084 [ 5] local 192.168.122.180 port 5201 connected to 192.168.122.1 port 52098 [ ID] Interval Transfer Bitrate [ 5] 0.00-1.00 sec 1.32 GBytes 11.3 Gbits/sec [ 5] 1.00-2.00 sec 1.19 GBytes 10.2 Gbits/sec [ 5] 2.00-3.00 sec 1.26 GBytes 10.8 Gbits/sec [ 5] 3.00-4.00 sec 1.36 GBytes 11.7 Gbits/sec [ 5] 4.00-5.00 sec 1.33 GBytes 11.4 Gbits/sec [ 5] 5.00-6.00 sec 1.21 GBytes 10.4 Gbits/sec [ 5] 6.00-7.00 sec 1.31 GBytes 11.2 Gbits/sec [ 5] 7.00-8.00 sec 1.25 GBytes 10.7 Gbits/sec [ 5] 8.00-9.00 sec 1.33 GBytes 11.5 Gbits/sec [ 5] 9.00-10.00 sec 1.24 GBytes 10.7 Gbits/sec [ 5] 10.00-10.04 sec 56.0 MBytes 12.1 Gbits/sec - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate [ 5] 0.00-10.04 sec 12.9 GBytes 11.0 Gbits/sec receiver ----------------------------------------------------------- Server listening on 5201 (test #2) ----------------------------------------------------------- ^Ciperf3: interrupt - the server has terminated logout [ perf record: Woken up 20 times to write data ] [ perf record: Captured and wrote 5.040 MB perf.data (33411 samples) ] jmaloy@freyr:~/passt$

The perf record confirms this result. Below, we can observe that the CPU spends significantly less time in the function ____sys_recvmsg() when we have offset support.

Without offset support: ---------------------- jmaloy@freyr:~/passt$ perf report -q --symbol-filter=do_syscall_64 -p ____sys_recvmsg -x --stdio -i perf.data | head -1 46.32% 0.00% passt.avx2 [kernel.vmlinux] [k] do_syscall_64 ____sys_recvmsg

With offset support: ---------------------- jmaloy@freyr:~/passt$ perf report -q --symbol-filter=do_syscall_64 -p ____sys_recvmsg -x --stdio -i perf.data | head -1 28.12% 0.00% passt.avx2 [kernel.vmlinux] [k] do_syscall_64 ____sys_recvmsg

Suggested-by: Paolo Abeni Reviewed-by: David Gibson Signed-off-by: Jon Maloy --- include/net/tcp.h | 1 + net/ipv4/af_inet.c | 1 + net/ipv4/tcp.c | 26 +++++++++++++++++++------- 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h index 87f0e6c2e1f2..7eca7f2ac102 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -357,6 +357,7 @@ void tcp_twsk_purge(struct list_head *net_exit_list, int family); ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags); +int tcp_set_peek_offset(struct sock *sk, int val); struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, gfp_t gfp, bool force_schedule);

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c index fb81de10d332..7a8b3a91257f 100644 --- a/net/ipv4/af_inet.c +++ b/net/ipv4/af_inet.c @@ -1068,6 +1068,7 @@ const struct proto_ops inet_stream_ops = { #endif .splice_eof = inet_splice_eof, .splice_read = tcp_splice_read, + .set_peek_off = tcp_set_peek_offset, .read_sock = tcp_read_sock, .read_skb = tcp_read_skb, .sendmsg_locked = tcp_sendmsg_locked, diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index fce5668a6a3d..ad03e0cee3c1 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -863,6 +863,14 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos, } EXPORT_SYMBOL(tcp_splice_read);

+int tcp_set_peek_offset(struct sock *sk, int val) +{ + WRITE_ONCE(sk->sk_peek_off, val); + + return 0; +} +EXPORT_SYMBOL(tcp_set_peek_offset); + struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, gfp_t gfp, bool force_schedule) { @@ -1414,8 +1422,6 @@ static int tcp_peek_sndq(struct sock *sk, struct msghdr *msg, int len) struct sk_buff *skb; int copied = 0, err = 0;

- /* XXX -- need to support SO_PEEK_OFF */ - skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { err = skb_copy_datagram_msg(skb, 0, msg, skb->len); if (err) @@ -2317,6 +2323,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, long timeo; struct sk_buff *skb, *last; u32 urg_hole = 0; + u32 peek_offset = 0;

err = -ENOTCONN; if (sk->sk_state == TCP_LISTEN) @@ -2349,7 +2356,8 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,

seq = &tp->copied_seq; if (flags & MSG_PEEK) { - peek_seq = tp->copied_seq; + peek_offset = max(sk_peek_offset(sk, flags), 0); + peek_seq = tp->copied_seq + peek_offset; seq = &peek_seq; }

@@ -2452,11 +2460,11 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, }

if ((flags & MSG_PEEK) && - (peek_seq - copied - urg_hole != tp->copied_seq)) { + (peek_seq - peek_offset - copied - urg_hole != tp->copied_seq)) { net_dbg_ratelimited("TCP(%s:%d): Application bug, race in MSG_PEEK\n", current->comm, task_pid_nr(current)); - peek_seq = tp->copied_seq; + peek_seq = tp->copied_seq + peek_offset; } continue;

@@ -2497,7 +2505,10 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, WRITE_ONCE(*seq, *seq + used); copied += used; len -= used; - + if (flags & MSG_PEEK) + sk_peek_offset_fwd(sk, used); + else + sk_peek_offset_bwd(sk, used); tcp_rcv_space_adjust(sk);

skip_copy: @@ -2774,6 +2785,7 @@ void __tcp_close(struct sock *sk, long timeout) data_was_unread += len; __kfree_skb(skb); } + sk_set_peek_off(sk, -1);

/* If socket has been already reset (e.g. in tcp_reset()) - kill it. */ if (sk->sk_state == TCP_CLOSE) @@ -4492,7 +4504,7 @@ void tcp_done(struct sock *sk) reqsk_fastopen_remove(sk, req, false);

WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK); - + sk_set_peek_off(sk, -1); if (!sock_flag(sk, SOCK_DEAD)) sk->sk_state_change(sk); else

On Thu, 2024-02-08 at 09:50 -0500, Jon Maloy wrote:

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index fce5668a6a3d..ad03e0cee3c1 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -863,6 +863,14 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos, } EXPORT_SYMBOL(tcp_splice_read);

+int tcp_set_peek_offset(struct sock *sk, int val) +{ + WRITE_ONCE(sk->sk_peek_off, val); + + return 0; +} +EXPORT_SYMBOL(tcp_set_peek_offset);

this looks equal to sk_set_peek_off. why not reusing the latter? [...]

@@ -2317,6 +2323,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, long timeo; struct sk_buff *skb, *last; u32 urg_hole = 0; + u32 peek_offset = 0;

Very minor nit: the variable definition should follow the reverse xmas tree order. Here such order is already broken, but I still place this definition just before 'urg_hole'.

err = -ENOTCONN; if (sk->sk_state == TCP_LISTEN) @@ -2774,6 +2785,7 @@ void __tcp_close(struct sock *sk, long timeout) data_was_unread += len; __kfree_skb(skb); } + sk_set_peek_off(sk, -1);

Why are you resetting the peek offset at close time? nobody can read or poll the socket at this point. You should instead reset it at tcp_disconnect() time.

/* If socket has been already reset (e.g. in tcp_reset()) - kill it. */ if (sk->sk_state == TCP_CLOSE) @@ -4492,7 +4504,7 @@ void tcp_done(struct sock *sk) reqsk_fastopen_remove(sk, req, false);

WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK); - + sk_set_peek_off(sk, -1);

Similar question here. tcp_done is called e.g. after an incoming reset() and the socket is still readable after an incoming reset, if there is pending data in the receive buffer. Resetting the peek offset could produce unexpected results for the reader. Cheers, Paolo