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Eric Dumazet 4d8b5fe1a4 net_sched: limit try_bulk_dequeue_skb() batches 
[ Upstream commit 0345552a65 ]

After commit 100dfa74ca ("inet: dev_queue_xmit() llist adoption")
I started seeing many qdisc requeues on IDPF under high TX workload.

$ tc -s qd sh dev eth1 handle 1: ; sleep 1; tc -s qd sh dev eth1 handle 1:
qdisc mq 1: root
 Sent 43534617319319 bytes 268186451819 pkt (dropped 0, overlimits 0 requeues 3532840114)
 backlog 1056Kb 6675p requeues 3532840114
qdisc mq 1: root
 Sent 43554665866695 bytes 268309964788 pkt (dropped 0, overlimits 0 requeues 3537737653)
 backlog 781164b 4822p requeues 3537737653

This is caused by try_bulk_dequeue_skb() being only limited by BQL budget.

perf record -C120-239 -e qdisc:qdisc_dequeue sleep 1 ; perf script
...
 netperf 75332 [146]  2711.138269: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1292 skbaddr=0xff378005a1e9f200
 netperf 75332 [146]  2711.138953: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1213 skbaddr=0xff378004d607a500
 netperf 75330 [144]  2711.139631: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1233 skbaddr=0xff3780046be20100
 netperf 75333 [147]  2711.140356: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1093 skbaddr=0xff37800514845b00
 netperf 75337 [151]  2711.141037: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1353 skbaddr=0xff37800460753300
 netperf 75337 [151]  2711.141877: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1367 skbaddr=0xff378004e72c7b00
 netperf 75330 [144]  2711.142643: qdisc:qdisc_dequeue: dequeue ifindex=5 qdisc handle=0x80150000 parent=0x10013 txq_state=0x0 packets=1202 skbaddr=0xff3780045bd60000
...

This is bad because :

1) Large batches hold one victim cpu for a very long time.

2) Driver often hit their own TX ring limit (all slots are used).

3) We call dev_requeue_skb()

4) Requeues are using a FIFO (q->gso_skb), breaking qdisc ability to
   implement FQ or priority scheduling.

5) dequeue_skb() gets packets from q->gso_skb one skb at a time
   with no xmit_more support. This is causing many spinlock games
   between the qdisc and the device driver.

Requeues were supposed to be very rare, lets keep them this way.

Limit batch sizes to /proc/sys/net/core/dev_weight (default 64) as
__qdisc_run() was designed to use.

Fixes: 5772e9a346 ("qdisc: bulk dequeue support for qdiscs with TCQ_F_ONETXQUEUE")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://patch.msgid.link/20251109161215.2574081-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-11-24 10:35:52 +01:00
arch riscv: acpi: avoid errors caused by probing DT devices when ACPI is used 2025-11-24 10:35:46 +01:00
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 net/mlx5e: Fix potentially misleading debug message 2025-11-24 10:35:52 +01:00
fs NFSD: Skip close replay processing if XDR encoding fails 2025-11-24 10:35:50 +01:00
include net_sched: act_connmark: use RCU in tcf_connmark_dump() 2025-11-24 10:35:51 +01:00
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 tracing: Fix memory leaks in create_field_var() 2025-11-13 15:34:39 -05:00
lib lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC 2025-11-13 15:34:40 -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_sched: limit try_bulk_dequeue_skb() batches 2025-11-24 10:35:52 +01:00
rust rust: Add -fno-isolate-erroneous-paths-dereference to bindgen_skip_c_flags 2025-11-24 10:35:49 +01:00
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 ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr 2025-11-13 15:34:32 -05:00
sound ASoC: max98090/91: fixed max98091 ALSA widget powering up/down 2025-11-24 10:35:48 +01:00
tools selftests: net: local_termination: Wait for interfaces to come up 2025-11-24 10:35:49 +01:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
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 6.12.58 2025-11-13 15:34:41 -05:00
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.