Add a packetdrill test to verify that locked SO_RCVBUF sockets do not suffer from scaling_ratio truesize penalties.
The test uses a standard 1460 MSS and sends medium-sized packets (600, 700, 800 bytes) to trigger the recalculation logic. It checks that the internal window clamp (tcpi_rcv_ssthresh) does not drop unexpectedly. Signed-off-by: Ankit Jain <[email protected]> --- .../net/packetdrill/tcp_locked_rcvbuf_sws.pkt | 29 +++++++++++++++++++ 1 file changed, 29 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_locked_rcvbuf_sws.pkt diff --git a/tools/testing/selftests/net/packetdrill/tcp_locked_rcvbuf_sws.pkt b/tools/testing/selftests/net/packetdrill/tcp_locked_rcvbuf_sws.pkt new file mode 100644 index 000000000000..43e1d00d5f26 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_locked_rcvbuf_sws.pkt @@ -0,0 +1,29 @@ +// SPDX-License-Identifier: GPL-2.0 +// Test that TCP does not reduce scaling_ratio for locked SO_RCVBUF. + +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 ++0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [32768], 4) = 0 ++0 bind(3, ..., ...) = 0 ++0 listen(3, 1) = 0 + +// Establish connection with standard MSS. ++0 < S 0:0(0) win 65535 <mss 1460,nop,wscale 8> ++0 > S. 0:0(0) ack 1 <...> ++0 < . 1:1(0) ack 1 win 65535 ++0 accept(3, ..., ...) = 4 + +// Inject varying payload sizes to force scaling_ratio recalculation. ++0.1 < P. 1:601(600) ack 1 win 65535 ++0 > . 1:1(0) ack 601 <...> + ++0.1 < P. 601:1301(700) ack 1 win 65535 ++0 > . 1:1(0) ack 1301 <...> + ++0.1 < P. 1301:2101(800) ack 1 win 65535 ++0 > . 1:1(0) ack 2101 <...> + +// Check that truesize penalty did not reduce the window clamp. +// On unpatched kernels, rcv_ssthresh drops to ~22K. ++0.1 %{ +assert tcpi_rcv_ssthresh > 28000, f"rcv_ssthresh dropped unexpectedly: {tcpi_rcv_ssthresh}" +}% -- 2.53.0
