From: Ilpo Järvinen ij@kernel.org
As SACK blocks tend to eat all option space when there are many holes, it is useful to compromise on sending many SACK blocks in every ACK and try to fit AccECN option there by reduction the number of SACK blocks. But never go below two SACK blocks because of AccECN option.
As AccECN option is often not put to every ACK, the space hijack is usually only temporary.
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 | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index af619233a6f3..a53eae6892b5 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -981,8 +981,21 @@ static int tcp_options_fit_accecn(struct tcp_out_options *opts, int required, opts->num_accecn_fields--; size -= TCPOLEN_ACCECN_PERFIELD; } - if (opts->num_accecn_fields < required) + if (opts->num_accecn_fields < required) { + if (opts->num_sack_blocks > 2) { + /* Try to fit the option by removing one SACK block */ + opts->num_sack_blocks--; + size = tcp_options_fit_accecn(opts, required, + remaining + + TCPOLEN_SACK_PERBLOCK, + max_combine_saving); + if (opts->options & OPTION_ACCECN) + return size - TCPOLEN_SACK_PERBLOCK; + + opts->num_sack_blocks++; + } return 0; + }
opts->options |= OPTION_ACCECN; return size;