On Thu, 2016-08-18 at 10:55 -0700, Yuchung Cheng wrote: > > + /* Reset SACK state. A conforming SACK implementation will > > + * do the same at a timeout based retransmit. When a connection > > + * is in a sad state like this, we care only about integrity > > + * of the connection not performance. > > + */ > > + if (tp->rx_opt.sack_ok) > > + tcp_sack_reset(&tp->rx_opt); > I am curious what if we don't reset. It seems SACK will continue to > function properly (at least for Linux sender). But this of course > belongs to a different patch / discussion. >
Agreed, we might try to be smarter here and update sack block if possible. BTW, here is the packetdrill test I used to test this patch : # cat sack-prune.pkt 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [2048], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7> +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 0> +0.100 < . 1:1(0) ack 1 win 1024 +0 accept(3, ..., ...) = 4 +0.01 < . 2:3(1) ack 1 win 1024 +0 > . 1:1(0) ack 1 <nop,nop, sack 2:3> +0.01 < . 4:5(1) ack 1 win 1024 +0 > . 1:1(0) ack 1 <nop,nop, sack 4:5 2:3> +0.01 < . 6:7(1) ack 1 win 1024 +0 > . 1:1(0) ack 1 <nop,nop, sack 6:7 4:5 2:3> +0.01 < . 8:9(1) ack 1 win 1024 +0 > . 1:1(0) ack 1 <nop,nop, sack 8:9 6:7 4:5 2:3> +0.01 < . 10:11(1) ack 1 win 1024 // Alas, we had to clean OFO queue, last skb (sequence 8:9) was dropped. +0 > . 1:1(0) ack 1 <nop,nop, sack 10:11> +0.01 < . 1:2(1) ack 1 win 1024 // Make sure kernel did not drop 2:3 sequence +0 > . 1:1(0) ack 3 <nop,nop, sack 10:11> +0 read(4, ..., 2) = 2 +0.01 < . 3:4(1) ack 1 win 1024 +0 > . 1:1(0) ack 5 <nop,nop, sack 10:11> +0.01 < . 5:6(1) ack 1 win 1024 +0 > . 1:1(0) ack 7 <nop,nop, sack 10:11> +0 read(4, ..., 4) = 4 +0.01 < . 7:8(1) ack 1 win 1024 +0 > . 1:1(0) ack 8 <nop,nop, sack 10:11> +0.01 < . 8:9(1) ack 1 win 1024 +0 > . 1:1(0) ack 9 <nop,nop, sack 10:11> +0.01 < . 9:10(1) ack 1 win 1024 +0 > . 1:1(0) ack 11
