On Tue, 6 May 2025, Ilpo Järvinen wrote:
On Tue, 29 Apr 2025, Paolo Abeni wrote:
On 4/22/25 5:35 PM, chia-yu.chang@nokia-bell-labs.com wrote:
@@ -1117,6 +1235,17 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb opts->num_sack_blocks = 0; }
- if (tcp_ecn_mode_accecn(tp) &&
sock_net(sk)->ipv4.sysctl_tcp_ecn_option) {int saving = opts->num_sack_blocks > 0 ? 2 : 0;int remaining = MAX_TCP_OPTION_SPACE - size;AFACS the above means tcp_options_fit_accecn() must clear any already set options, but apparently it does not do so. Have you tested with something adding largish options like mptcp?
This "fitting" for AccEcn option is not to make room for the option but to check if AccECN option fits and in what length, and how it can take advantage of some nop bytes when available to save option space.
A minor correction. SACK blocks will naturally fill the entire option space if there are enough holes which would "starve" AccECN from using option space during loss recovery. Thus, AccECN option is allowed allowed grab some of that space from SACK. There's redundancy in SACK blocks anyway so it shouldn't usually impact SACK signal much.