From linux-6.9.0 the kernel will contain
commit 05ea491641d3 ("tcp: add support for SO_PEEK_OFF socket option").
This new feature makes is possible to call recv_msg(MSG_PEEK) and make
it start reading data from a given offset set by the SO_PEEK_OFF socket
option. This way, we can avoid repeated reading of already read bytes of
a received message, hence saving read cycles when forwarding TCP messages
in the host->name space direction.
In this commit, we add functionality to leverage this feature when
available, while we fall back to the previous behavior when not.
Measurements with iperf3 shows that throughput increases with 15-20 percent
in the host->namespace direction when this feature is used.
Signed-off-by: Jon Maloy <jmaloy(a)redhat.com>
---
v2: - Some smaller changes as suggested by David Gibson and Stefano Brivio.
- Moved set_peek_offset() to only the locations where the socket is set
to ESTABLISHED.
- Removed the per-packet synchronization between sk_peek_off and
already_sent. Instead only doing it in retransmit situations.
- The problem I found when trouble shooting the occasionally occurring
out of synch values between 'already_sent' and 'sk_peek_offset'
may
have deeper implications that we may need to be investigate.
---
tcp.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 55 insertions(+), 3 deletions(-)
diff --git a/tcp.c b/tcp.c
index 905d26f..535f1a2 100644
--- a/tcp.c
+++ b/tcp.c
@@ -513,6 +513,9 @@ static struct iovec tcp6_l2_iov [TCP_FRAMES_MEM];
static struct iovec tcp4_l2_flags_iov [TCP_FRAMES_MEM];
static struct iovec tcp6_l2_flags_iov [TCP_FRAMES_MEM];
+/* Does the kernel support TCP_PEEK_OFF? */
+static bool peek_offset_cap;
+
/* sendmsg() to socket */
static struct iovec tcp_iov [UIO_MAXIOV];
@@ -582,6 +585,22 @@ static_assert(ARRAY_SIZE(tc_hash) >= FLOW_MAX,
int init_sock_pool4 [TCP_SOCK_POOL_SIZE];
int init_sock_pool6 [TCP_SOCK_POOL_SIZE];
+/**
+ * set_peek_offset() - Set SO_PEEK_OFF offset on a socket if supported
+ * @conn Connection struct with reference to socket and flags
+ * @offset Offset in bytes
+ */
+static void set_peek_offset(struct tcp_tap_conn *conn, int offset)
+{
+ int s;
+
+ if (!peek_offset_cap)
+ return;
+ s = conn->sock;
+ if (setsockopt(s, SOL_SOCKET, SO_PEEK_OFF, &offset, sizeof(offset)))
+ perror("Failed to set SO_PEEK_OFF\n");
+}
+
/**
* tcp_conn_epoll_events() - epoll events mask for given connection state
* @events: Current connection events
@@ -2174,6 +2193,12 @@ static int tcp_data_from_sock(struct ctx *c, struct tcp_tap_conn
*conn)
if (iov_rem)
iov_sock[fill_bufs].iov_len = iov_rem;
+ if (peek_offset_cap) {
+ /* Don't use discard buffer */
+ mh_sock.msg_iov = &iov_sock[1];
+ mh_sock.msg_iovlen -= 1;
+ }
+
/* Receive into buffers, don't dequeue until acknowledged by guest. */
do
len = recvmsg(s, &mh_sock, MSG_PEEK);
@@ -2195,7 +2220,10 @@ static int tcp_data_from_sock(struct ctx *c, struct tcp_tap_conn
*conn)
return 0;
}
- sendlen = len - already_sent;
+ sendlen = len;
+ if (!peek_offset_cap)
+ sendlen -= already_sent;
+
if (sendlen <= 0) {
conn_flag(c, conn, STALLED);
return 0;
@@ -2365,9 +2393,17 @@ static int tcp_data_from_tap(struct ctx *c, struct tcp_tap_conn
*conn,
flow_trace(conn,
"fast re-transmit, ACK: %u, previous sequence: %u",
max_ack_seq, conn->seq_to_tap);
+
+ /* Ensure seq_from_tap isn't updated twice after call */
+ tcp_l2_data_buf_flush(c);
+
conn->seq_ack_from_tap = max_ack_seq;
conn->seq_to_tap = max_ack_seq;
+ set_peek_offset(conn, 0);
tcp_data_from_sock(c, conn);
+
+ /* Empty queue before any POLL event tries to send it again */
+ tcp_l2_data_buf_flush(c);
}
if (!iov_i)
@@ -2459,6 +2495,7 @@ static void tcp_conn_from_sock_finish(struct ctx *c, struct
tcp_tap_conn *conn,
conn->seq_ack_to_tap = conn->seq_from_tap;
conn_event(c, conn, ESTABLISHED);
+ set_peek_offset(conn, 0);
/* The client might have sent data already, which we didn't
* dequeue waiting for SYN,ACK from tap -- check now.
@@ -2539,6 +2576,7 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, int af,
goto reset;
conn_event(c, conn, ESTABLISHED);
+ set_peek_offset(conn, 0);
if (th->fin) {
conn->seq_from_tap++;
@@ -2705,7 +2743,7 @@ void tcp_listen_handler(struct ctx *c, union epoll_ref ref,
struct sockaddr_storage sa;
socklen_t sl = sizeof(sa);
union flow *flow;
- int s;
+ int s = 0;
if (c->no_tcp || !(flow = flow_alloc()))
return;
@@ -2767,7 +2805,10 @@ void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
flow_dbg(conn, "ACK timeout, retry");
conn->retrans++;
conn->seq_to_tap = conn->seq_ack_from_tap;
+ set_peek_offset(conn, 0);
+ tcp_l2_data_buf_flush(c);
tcp_data_from_sock(c, conn);
+ tcp_l2_data_buf_flush(c);
tcp_timer_ctl(c, conn);
}
} else {
@@ -3041,7 +3082,8 @@ static void tcp_sock_refill_init(const struct ctx *c)
*/
int tcp_init(struct ctx *c)
{
- unsigned b;
+ unsigned int b, optv = 0;
+ int s;
for (b = 0; b < TCP_HASH_TABLE_SIZE; b++)
tc_hash[b] = FLOW_SIDX_NONE;
@@ -3065,6 +3107,16 @@ int tcp_init(struct ctx *c)
NS_CALL(tcp_ns_socks_init, c);
}
+ /* Probe for SO_PEEK_OFF support */
+ s = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP);
+ if (s < 0) {
+ warn("Temporary TCP socket creation failed");
+ } else {
+ if (!setsockopt(s, SOL_SOCKET, SO_PEEK_OFF, &optv, sizeof(int)))
+ peek_offset_cap = true;
+ close(s);
+ }
+ debug("SO_PEEK_OFF%ssupported", peek_offset_cap ? " " : " not
");
return 0;
}
--
2.42.0