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Eric Dumazet 562bcdc0d7 net: call cond_resched() less often in __release_sock() [ Upstream commit `16c610162d` ] While stress testing TCP I had unexpected retransmits and sack packets when a single cpu receives data from multiple high-throughput flows. super_netperf 4 -H srv -T,10 -l 3000 & Tcpdump extract: 00:00:00.000007 IP6 clnt > srv: Flags [.], seq 26062848:26124288, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 61440 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26124288:26185728, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [P.], seq 26185728:26243072, ack 1, win 66, options [nop,nop,TS val 651460834 ecr 3100749131], length 57344 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26243072:26304512, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [.], seq 26304512:26365952, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 61440 00:00:00.000007 IP6 clnt > srv: Flags [P.], seq 26365952:26423296, ack 1, win 66, options [nop,nop,TS val 651460844 ecr 3100749141], length 57344 00:00:00.000006 IP6 clnt > srv: Flags [.], seq 26423296:26484736, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [.], seq 26484736:26546176, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 61440 00:00:00.000005 IP6 clnt > srv: Flags [P.], seq 26546176:26603520, ack 1, win 66, options [nop,nop,TS val 651460853 ecr 3100749150], length 57344 00:00:00.003932 IP6 clnt > srv: Flags [P.], seq 26603520:26619904, ack 1, win 66, options [nop,nop,TS val 651464844 ecr 3100753141], length 16384 00:00:00.006602 IP6 clnt > srv: Flags [.], seq 24862720:24866816, ack 1, win 66, options [nop,nop,TS val 651471419 ecr 3100759716], length 4096 00:00:00.013000 IP6 clnt > srv: Flags [.], seq 24862720:24866816, ack 1, win 66, options [nop,nop,TS val 651484421 ecr 3100772718], length 4096 00:00:00.000416 IP6 srv > clnt: Flags [.], ack 26619904, win 1393, options [nop,nop,TS val 3100773185 ecr 651484421,nop,nop,sack 1 {24862720:24866816}], length 0 After analysis, it appears this is because of the cond_resched() call from __release_sock(). When current thread is yielding, while still holding the TCP socket lock, it might regain the cpu after a very long time. Other peer TLP/RTO is firing (multiple times) and packets are retransmit, while the initial copy is waiting in the socket backlog or receive queue. In this patch, I call cond_resched() only once every 16 packets. Modern TCP stack now spends less time per packet in the backlog, especially because ACK are no longer sent (commit `133c4c0d37` "tcp: defer regular ACK while processing socket backlog") Before: clnt:/# nstat -n;sleep 10;nstat\|egrep "TcpOutSegs\|TcpRetransSegs\|TCPFastRetrans\|TCPTimeouts\|Probes\|TCPSpuriousRTOs\|DSACK" TcpOutSegs 19046186 0.0 TcpRetransSegs 1471 0.0 TcpExtTCPTimeouts 1397 0.0 TcpExtTCPLossProbes 1356 0.0 TcpExtTCPDSACKRecv 1352 0.0 TcpExtTCPSpuriousRTOs 114 0.0 TcpExtTCPDSACKRecvSegs 1352 0.0 After: clnt:/# nstat -n;sleep 10;nstat\|egrep "TcpOutSegs\|TcpRetransSegs\|TCPFastRetrans\|TCPTimeouts\|Probes\|TCPSpuriousRTOs\|DSACK" TcpOutSegs 19218936 0.0 Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20250903174811.1930820-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		History 2025-11-13 15:34:19 -05:00
arch	mips: lantiq: danube: rename stp node on EASY50712 reference board	2025-11-13 15:34:17 -05:00
block	blk-cgroup: fix possible deadlock while configuring policy	2025-11-13 15:34:07 -05:00
certs	sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3	2024-09-20 19:52:48 +03:00
crypto	crypto: essiv - Check ssize for decryption and in-place encryption	2025-10-19 16:33:42 +02:00
Documentation	dpll: spec: add missing module-name and clock-id to pin-get reply	2025-11-13 15:33:59 -05:00
drivers	drm/xe/guc: Set upper limit of H2G retries over CTB	2025-11-13 15:34:19 -05:00
fs	fuse: zero initialize inode private data	2025-11-13 15:34:15 -05:00
include	net: nfc: nci: Increase NCI_DATA_TIMEOUT to 3000 ms	2025-11-13 15:34:18 -05:00
init	init: handle bootloader identifier in kernel parameters	2025-10-19 16:33:50 +02:00
io_uring	io_uring/zctx: check chained notif contexts	2025-11-13 15:34:03 -05:00
ipc	ipc: fix to protect IPCS lookups using RCU	2025-06-27 11:11:22 +01:00
kernel	uprobe: Do not emulate/sstep original instruction when ip is changed	2025-11-13 15:34:07 -05:00
lib	kunit: test_dev_action: Correctly cast 'priv' pointer to long*	2025-11-13 15:33:57 -05:00
LICENSES	LICENSES: add 0BSD license text	2024-09-01 20:43:24 -07:00
mm	mm: prevent poison consumption when splitting THP	2025-10-29 14:08:57 +01:00
net	net: call cond_resched() less often in __release_sock()	2025-11-13 15:34:19 -05:00
rust	mm/ksm: fix flag-dropping behavior in ksm_madvise	2025-10-23 16:20:47 +02:00
samples	ftrace/samples: Fix function size computation	2025-09-19 16:35:44 +02:00
scripts	gcc-plugins: Remove TODO_verify_il for GCC >= 16	2025-10-06 11:17:52 +02:00
security	KEYS: trusted_tpm1: Compare HMAC values in constant time	2025-10-19 16:33:51 +02:00
sound	ALSA: usb-audio: apply quirk for MOONDROP Quark2	2025-11-13 15:34:19 -05:00
tools	selftests: drv-net: rss_ctx: make the test pass with few queues	2025-11-13 15:34:18 -05:00
usr	kbuild: hdrcheck: fix cross build with clang	2025-03-13 13:02:18 +01:00
virt	KVM: Allow CPU to reschedule while setting per-page memory attributes	2025-07-17 18:37:08 +02:00
.clang-format	clang-format: Update with v6.11-rc1's `for_each` macro list	2024-08-02 13:20:31 +02:00
.clippy.toml	rust: give Clippy the minimum supported Rust version	2025-08-01 09:48:44 +01:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.editorconfig	.editorconfig: remove trim_trailing_whitespace option	2024-06-13 16:47:52 +02:00
.get_maintainer.ignore	Add Jeff Kirsher to .get_maintainer.ignore	2024-03-08 11:36:54 +00:00
.gitattributes	.gitattributes: set diff driver for Rust source code files	2023-05-31 17:48:25 +02:00
.gitignore	rust: introduce `.clippy.toml`	2025-03-13 13:01:42 +01:00
.mailmap	mailmap: add entry for Thorsten Blum	2024-11-07 14:14:59 -08:00
.rustfmt.toml	rust: add `.rustfmt.toml`	2022-09-28 09:02:20 +02:00
COPYING	COPYING: state that all contributions really are covered by this file	2020-02-10 13:32:20 -08:00
CREDITS	MAINTAINERS: Remove self from DSA entry	2024-11-03 12:52:38 -08:00
Kbuild	Kbuild updates for v6.1	2022-10-10 12:00:45 -07:00
Kconfig	kbuild: ensure full rebuild when the compiler is updated	2020-05-12 13:28:33 +09:00
MAINTAINERS	MAINTAINERS: Update Alexey Makhalov's email address	2025-05-22 14:29:46 +02:00
Makefile	Linux 6.12.57	2025-11-02 22:15:23 +09:00
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
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In order to build the documentation, use ``make htmldocs`` or
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    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.