On Thu, May 17, 2018 at 2:57 PM, Neal Cardwell <ncardw...@google.com> wrote: > On Thu, May 17, 2018 at 5:47 PM Eric Dumazet <eduma...@google.com> wrote: > >> When TCP receives an out-of-order packet, it immediately sends >> a SACK packet, generating network load but also forcing the >> receiver to send 1-MSS pathological packets, increasing its >> RTX queue length/depth, and thus processing time. > >> Wifi networks suffer from this aggressive behavior, but generally >> speaking, all these SACK packets add fuel to the fire when networks >> are under congestion. > >> This patch adds a high resolution timer and tp->compressed_ack counter. > >> Instead of sending a SACK, we program this timer with a small delay, >> based on RTT and capped to 1 ms : > >> delay = min ( 5 % of RTT, 1 ms) > >> If subsequent SACKs need to be sent while the timer has not yet >> expired, we simply increment tp->compressed_ack. > >> When timer expires, a SACK is sent with the latest information. >> Whenever an ACK is sent (if data is sent, or if in-order >> data is received) timer is canceled. > >> Note that tcp_sack_new_ofo_skb() is able to force a SACK to be sent >> if the sack blocks need to be shuffled, even if the timer has not >> expired. > >> A new SNMP counter is added in the following patch. > >> Two other patches add sysctls to allow changing the 1,000,000 and 44 >> values that this commit hard-coded. > >> Signed-off-by: Eric Dumazet <eduma...@google.com> >> --- > > Very nice. I like the constants and the min(rcv_rtt, srtt). > > Acked-by: Neal Cardwell <ncardw...@google.com> Acked-by: Yuchung Cheng <ych...@google.com>
Great work. Hopefully this would save middle-boxes' from handling TCP-ACK themselves. > > Thanks! > > neal
