From: Ilpo Järvinen ij@kernel.org
There is some waste space in the option usage due to padding of 32-bit fields. AccECN option can take advantage of those few bytes as its tail is often consuming just a few odd bytes.
Signed-off-by: Ilpo Järvinen ij@kernel.org Signed-off-by: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com --- net/ipv4/tcp_output.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index fa7facec04ed..87a2a20243c7 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -709,6 +709,8 @@ static __be32 *process_tcp_ao_options(struct tcp_sock *tp, return ptr; }
+#define NOP_LEFTOVER ((TCPOPT_NOP << 8) | TCPOPT_NOP) + /* Write previously computed TCP options to the packet. * * Beware: Something in the Internet is very sensitive to the ordering of @@ -727,8 +729,10 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, struct tcp_out_options *opts, struct tcp_key *key) { + u16 leftover_bytes = NOP_LEFTOVER; /* replace next NOPs if avail */ __be32 *ptr = (__be32 *)(th + 1); u16 options = opts->options; /* mungable copy */ + int leftover_size = 2;
if (tcp_key_is_md5(key)) { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | @@ -763,17 +767,22 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, }
if (unlikely(OPTION_SACK_ADVERTISE & options)) { - *ptr++ = htonl((TCPOPT_NOP << 24) | - (TCPOPT_NOP << 16) | + *ptr++ = htonl((leftover_bytes << 16) | (TCPOPT_SACK_PERM << 8) | TCPOLEN_SACK_PERM); + leftover_bytes = NOP_LEFTOVER; }
if (unlikely(OPTION_WSCALE & options)) { - *ptr++ = htonl((TCPOPT_NOP << 24) | + u8 highbyte = TCPOPT_NOP; + + if (unlikely(leftover_size == 1)) + highbyte = leftover_bytes >> 8; + *ptr++ = htonl((highbyte << 24) | (TCPOPT_WINDOW << 16) | (TCPOLEN_WINDOW << 8) | opts->ws); + leftover_bytes = NOP_LEFTOVER; }
if (unlikely(opts->num_sack_blocks)) { @@ -781,8 +790,7 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, tp->duplicate_sack : tp->selective_acks; int this_sack;
- *ptr++ = htonl((TCPOPT_NOP << 24) | - (TCPOPT_NOP << 16) | + *ptr++ = htonl((leftover_bytes << 16) | (TCPOPT_SACK << 8) | (TCPOLEN_SACK_BASE + (opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK))); @@ -794,6 +802,10 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, }
tp->rx_opt.dsack = 0; + } else if (unlikely(leftover_bytes != NOP_LEFTOVER)) { + *ptr++ = htonl((leftover_bytes << 16) | + (TCPOPT_NOP << 8) | + TCPOPT_NOP); }
if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {