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> Thanks! neal
