| Message ID | 20240406182107.261472-2-jmaloy@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | tcp: add support for SO_PEEK_OFF socket option | expand |
On Sat, Apr 6, 2024 at 8:21 PM <jmaloy@redhat.com> wrote: > > From: Jon Maloy <jmaloy@redhat.com> > > 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. > > j > ----------------------------------------------------------- > 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 <pabeni@redhat.com> > Reviewed-by: Stefano Brivio <sbrivio@redhat.com> > Signed-off-by: Jon Maloy <jmaloy@redhat.com> > > --- > v3: - Applied changes suggested by Stefano Brivio and Paolo Abeni > v4: - Same as v3. Posting was delayed because I first had to debug > an issue that turned out to not be directly related to this > change. See next commit in this series. This other issue is orthogonal, and might take more time. SO_RCVLOWAT had a similar issue, please take a look at what we did there. If you need SO_PEEK_OFF support, I would suggest you submit this patch as a standalone one. Reviewed-by: Eric Dumazet <edumazet@google.com> Thanks.
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c index 55bd72997b31..a7cfeda28bb2 100644 --- a/net/ipv4/af_inet.c +++ b/net/ipv4/af_inet.c @@ -1072,6 +1072,7 @@ const struct proto_ops inet_stream_ops = { #endif .splice_eof = inet_splice_eof, .splice_read = tcp_splice_read, + .set_peek_off = sk_set_peek_off, .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 92ee60492314..c0d6fd576d32 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1416,8 +1416,6 @@ 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) @@ -2328,6 +2326,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, int target; /* Read at least this many bytes */ long timeo; struct sk_buff *skb, *last; + u32 peek_offset = 0; u32 urg_hole = 0; err = -ENOTCONN; @@ -2361,7 +2360,8 @@ 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; } @@ -2464,11 +2464,11 @@ 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; @@ -2509,7 +2509,10 @@ 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: @@ -3010,6 +3013,7 @@ int tcp_disconnect(struct sock *sk, int flags) __skb_queue_purge(&sk->sk_receive_queue); WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); WRITE_ONCE(tp->urg_data, 0); + sk_set_peek_off(sk, -1); tcp_write_queue_purge(sk); tcp_fastopen_active_disable_ofo_check(sk); skb_rbtree_purge(&tp->out_of_order_queue);