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Eric Dumazet 416dd649f3 tcp: add net.ipv4.tcp_comp_sack_rtt_percent TCP SACK compression has been added in 2018 in commit `5d9f4262b7` ("tcp: add SACK compression"). It is working great for WAN flows (with large RTT). Wifi in particular gets a significant boost _when_ ACK are suppressed. Add a new sysctl so that we can tune the very conservative 5 % value that has been used so far in this formula, so that small RTT flows can benefit from this feature. delay = min ( 5 % of RTT, 1 ms) This patch adds new tcp_comp_sack_rtt_percent sysctl to ease experiments and tuning. Given that we cap the delay to 1ms (tcp_comp_sack_delay_ns sysctl), set the default value to 33 %. Quoting Neal Cardwell ( https://lore.kernel.org/netdev/CADVnQymZ1tFnEA1Q=vtECs0=Db7zHQ8=+WCQtnhHFVbEOzjVnQ@mail.gmail.com/ ) The rationale for 33% is basically to try to facilitate pipelining, where there are always at least 3 ACKs and 3 GSO/TSO skbs per SRTT, so that the path can maintain a budget for 3 full-sized GSO/TSO skbs "in flight" at all times: + 1 skb in the qdisc waiting to be sent by the NIC next + 1 skb being sent by the NIC (being serialized by the NIC out onto the wire) + 1 skb being received and aggregated by the receiver machine's aggregation mechanism (some combination of LRO, GRO, and sack compression) Note that this is basically the same magic number (3) and the same rationales as: (a) tcp_tso_should_defer() ensuring that we defer sending data for no longer than cwnd/tcp_tso_win_divisor (where tcp_tso_win_divisor = 3), and (b) bbr_quantization_budget() ensuring that cwnd is at least 3 GSO/TSO skbs to maintain pipelining and full throughput at low RTTs Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Neal Cardwell <ncardwell@google.com> Link: https://patch.msgid.link/20251106115236.3450026-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>		2025-11-07 18:41:44 -08:00
arch	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2025-11-06 09:27:40 -08:00
block	block-6.18-20251031	2025-10-31 12:57:19 -07:00
certs	sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3	2024-09-20 19:52:48 +03:00
crypto	net: Convert proto_ops bind() callbacks to use sockaddr_unsized	2025-11-04 19:10:32 -08:00
Documentation	tcp: add net.ipv4.tcp_comp_sack_rtt_percent	2025-11-07 18:41:44 -08:00
drivers	net: ravb: Use common defines for time stamping control	2025-11-06 17:38:26 -08:00
fs	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2025-11-06 09:27:40 -08:00
include	tcp: add net.ipv4.tcp_comp_sack_rtt_percent	2025-11-07 18:41:44 -08:00
init	printk changes for 6.18	2025-10-04 11:13:11 -07:00
io_uring	io_uring: fix buffer auto-commit for multishot uring_cmd	2025-10-23 19:41:31 -06:00
ipc	namespace-6.18-rc1	2025-09-29 11:20:29 -07:00
kernel	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2025-11-06 09:27:40 -08:00
lib	Second round of Kbuild fixes for 6.19	2025-11-01 10:00:53 -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-rc3	2025-10-24 12:40:51 -07:00
net	tcp: add net.ipv4.tcp_comp_sack_rtt_percent	2025-11-07 18:41:44 -08:00
rust	rust: kbuild: workaround `rustdoc` doctests modifier bug	2025-11-04 00:00:06 +01:00
samples	net: Convert proto_ops connect() callbacks to use sockaddr_unsized	2025-11-04 19:10:32 -08:00
scripts	kconfig/nconf: Initialize the default locale at startup	2025-11-01 00:23:22 -04:00
security	integrity-v6.18	2025-10-05 10:48:33 -07:00
sound	ASoC: Fixes for v6.18	2025-10-30 13:08:08 +01:00
tools	selftest: packetdrill: Add max RTO test for SYN+ACK.	2025-11-07 18:05:26 -08:00
usr	gen_init_cpio: Ignore fsync() returning EINVAL on pipes	2025-10-07 09:53:05 -07:00
virt	KVM x86 fixes for 6.18:	2025-10-18 10:25:43 +02:00
.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	linux_kselftest-kunit-fixes-6.18-rc4	2025-10-30 19:11:27 -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	MAINTAINERS: mark ISDN subsystem as orphan	2025-10-27 17:49:45 -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	net: dsa: add tagging driver for MaxLinear GSW1xx switch family	2025-11-06 14:16:17 -08:00
Makefile	Linux 6.18-rc4	2025-11-02 11:28:02 -08:00
README	README: Fix spelling	2024-03-18 03:36:32 -06:00

README

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.