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tcp: leverage support of SO_PEEK_OFF socket option when available

Browse source 
>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.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Jon Maloy 2024-07-12 15:04:49 -04:00 • committed by Stefano Brivio
parent 8bd57bf25b
commit e63d281871
3 changed files with 73 additions and 9 deletions

25
tcp_buf.c
View file

@ -408,6 +408,7 @@ int tcp_buf_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn)
uint32_t already_sent, seq;
struct iovec *iov;
/* How much have we read/sent since last received ack ? */
already_sent = conn->seq_to_tap - conn->seq_ack_from_tap;
if (SEQ_LT(already_sent, 0)) {
@ -416,6 +417,10 @@ int tcp_buf_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn)
conn->seq_ack_from_tap, conn->seq_to_tap);
conn->seq_to_tap = conn->seq_ack_from_tap;
already_sent = 0;
if (tcp_set_peek_offset(s, 0)) {
tcp_rst(c, conn);
return -1;
}
}
if (!wnd_scaled || already_sent >= wnd_scaled) {
@ -433,11 +438,16 @@ int tcp_buf_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn)
iov_rem = (wnd_scaled - already_sent) % mss;
}
mh_sock.msg_iov = iov_sock;
mh_sock.msg_iovlen = fill_bufs + 1;
iov_sock[0].iov_base = tcp_buf_discard;
iov_sock[0].iov_len = already_sent;
/* Prepare iov according to kernel capability */
if (!peek_offset_cap) {
mh_sock.msg_iov = iov_sock;
iov_sock[0].iov_base = tcp_buf_discard;
iov_sock[0].iov_len = already_sent;
mh_sock.msg_iovlen = fill_bufs + 1;
} else {
mh_sock.msg_iov = &iov_sock[1];
mh_sock.msg_iovlen = fill_bufs;
}
if (( v4 && tcp4_payload_used + fill_bufs > TCP_FRAMES_MEM) ||
(!v4 && tcp6_payload_used + fill_bufs > TCP_FRAMES_MEM)) {
@ -478,7 +488,10 @@ int tcp_buf_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;