tools/testing/selftests/net/packetdrill/tcp_slow_start_slow-start-fq-ack-per-2pkt.pkt

Source file repositories/reference/linux-study-clean/tools/testing/selftests/net/packetdrill/tcp_slow_start_slow-start-fq-ack-per-2pkt.pkt

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/net/packetdrill/tcp_slow_start_slow-start-fq-ack-per-2pkt.pkt
Extension
.pkt
Size
2255 bytes
Lines
64
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: tools
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
// Test of slow start when not application-limited, so that
// the cwnd continues to grow, even if TSQ triggers.
// In this variant, the receiver ACKs every other packet,
// approximating standard delayed ACKs.

// Note we use FQ/pacing to check if TCP Small Queues is not hurting

`./defaults.sh
tc qdisc replace dev tun0 root fq
sysctl -q net/ipv4/tcp_pacing_ss_ratio=200
sysctl -e -q net.ipv4.tcp_min_tso_segs=2`

    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

  +.1 < S 0:0(0) win 32792 <mss 1460,sackOK,nop,nop,nop,wscale 7>
   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
  +.1 < . 1:1(0) ack 1 win 500
   +0 accept(3, ..., ...) = 4
   +0 setsockopt(4, SOL_SOCKET, SO_SNDBUF, [200000], 4) = 0

   +0 write(4, ..., 40000) = 40000
// This might change if we cook the initial packet with 10 MSS.
   +0 > P. 1:2921(2920) ack 1
   +0 > P. 2921:5841(2920) ack 1
   +0 > P. 5841:8761(2920) ack 1
   +0 > P. 8761:11681(2920) ack 1
   +0 > P. 11681:14601(2920) ack 1
   +0 %{ assert tcpi_snd_cwnd == 10, tcpi_snd_cwnd }%

+.105 < . 1:1(0) ack 2921 win 500
   +0 %{ assert tcpi_snd_cwnd == 12, tcpi_snd_cwnd }%

// Note: after this commit : "net_sched: sch_fq: account for schedule/timers drifts"
// FQ notices that this packet missed the 'time to send next packet' computed
// when prior packet (11681:14601(2920)) was sent.
// So FQ will allow following packet to be sent a bit earlier (quantum/2)
// (FQ commit allows an application/cwnd limited flow to get at most quantum/2 extra credit)
   +0 > P. 14601:17521(2920) ack 1

+.003 < . 1:1(0) ack 5841 win 500
   +0 %{ assert tcpi_snd_cwnd == 14, tcpi_snd_cwnd }%

+.001 > P. 17521:20441(2920) ack 1

+.001 < . 1:1(0) ack 8761 win 500
   +0 %{ assert tcpi_snd_cwnd == 16, tcpi_snd_cwnd }%

// remaining packets are delivered at a constant rate.
+.007 > P. 20441:23361(2920) ack 1

+.002 < . 1:1(0) ack 11681 win 500
   +0 %{ assert tcpi_snd_cwnd == 18, tcpi_snd_cwnd }%
+.001 < . 1:1(0) ack 14601 win 500

+.004 > P. 23361:26281(2920) ack 1

+.007 > P. 26281:29201(2920) ack 1

   +0 %{ assert tcpi_snd_cwnd == 20, 'cwnd=%d' % tcpi_snd_cwnd }%

Annotation

Implementation Notes