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Eric Dumazet 295ce1eb36 tcp: fix tcp_tso_should_defer() vs large RTT
Neal reported that using neper tcp_stream with TCP_TX_DELAY
set to 50ms would often lead to flows stuck in a small cwnd mode,
regardless of the congestion control.

While tcp_stream sets TCP_TX_DELAY too late after the connect(),
it highlighted two kernel bugs.

The following heuristic in tcp_tso_should_defer() seems wrong
for large RTT:

delta = tp->tcp_clock_cache - head->tstamp;
/* If next ACK is likely to come too late (half srtt), do not defer */
if ((s64)(delta - (u64)NSEC_PER_USEC * (tp->srtt_us >> 4)) < 0)
      goto send_now;

If next ACK is expected to come in more than 1 ms, we should
not defer because we prefer a smooth ACK clocking.

While blamed commit was a step in the good direction, it was not
generic enough.

Another patch fixing TCP_TX_DELAY for established flows
will be proposed when net-next reopens.

Fixes: 50c8339e92 ("tcp: tso: restore IW10 after TSO autosizing")
Reported-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Tested-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20251011115742.1245771-1-edumazet@google.com
[pabeni@redhat.com: fixed whitespace issue]
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2025-10-14 12:21:48 +02:00
arch more s390 updates for 6.18 merge window 2025-10-09 10:51:43 -07:00
block Summary of significant series in this pull request: 2025-10-02 18:18:33 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-08 09:38:31 -07:00
Documentation doc: fix seg6_flowlabel path 2025-10-12 22:51:37 +01:00
drivers r8152: add error handling in rtl8152_driver_init 2025-10-14 12:07:21 +02:00
fs for-6.18-tag 2025-10-06 13:53:19 -07:00
include net/ip6_tunnel: Prevent perpetual tunnel growth 2025-10-13 17:43:46 -07:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring Summary of significant series in this pull request: 2025-10-02 18:18:33 -07:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel hyperv-next for v6.18 2025-10-07 08:40:15 -07:00
lib integrity-v6.18 2025-10-05 10:48:33 -07:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm slab fixes for 6.18-rc1 2025-10-09 10:33:50 -07:00
net tcp: fix tcp_tso_should_defer() vs large RTT 2025-10-14 12:21:48 +02:00
rust More power management updates for 6.18-rc1 2025-10-07 09:39:51 -07:00
samples Char/Misc/IIO/Binder changes for 6.18-rc1 2025-10-04 16:26:32 -07:00
scripts kconfig: Avoid prompting for transitional symbols 2025-10-07 08:21:23 -07:00
security integrity-v6.18 2025-10-05 10:48:33 -07:00
sound platform-drivers-x86 for v6.18-1 2025-10-04 15:28:18 -07:00
tools selftests: drv-net: update remaining Python init files 2025-10-12 19:03:53 +01:00
usr gen_init_cpio: add -a <data_align> as reflink optimization 2025-08-20 16:02:56 -07:00
virt hyperv-next for v6.18 2025-10-07 08:40:15 -07:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap VFIO updates for v6.18-rc1 2025-10-04 08:24:54 -07:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS USB/Thunderbolt changes for 6.18-rc1 2025-10-04 16:07:08 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS perf tools improvements and fixes for Linux v6.18: 2025-10-08 19:24:24 -07:00
Makefile It has been a relatively busy cycle in docsland, with changes all over: 2025-10-03 17:16:13 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.