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Christoph Paasch f80a71a29f net: When removing nexthops, don't call synchronize_net if it is not necessary 
[ Upstream commit b0ac6d3b56 ]

When removing a nexthop, commit
90f33bffa3 ("nexthops: don't modify published nexthop groups") added a
call to synchronize_rcu() (later changed to _net()) to make sure
everyone sees the new nexthop-group before the rtnl-lock is released.

When one wants to delete a large number of groups and nexthops, it is
fastest to first flush the groups (ip nexthop flush groups) and then
flush the nexthops themselves (ip -6 nexthop flush). As that way the
groups don't need to be rebalanced.

However, `ip -6 nexthop flush` will still take a long time if there is
a very large number of nexthops because of the call to
synchronize_net(). Now, if there are no more groups, there is no point
in calling synchronize_net(). So, let's skip that entirely by checking
if nh->grp_list is empty.

This gives us a nice speedup:

BEFORE:
=======

$ time sudo ip -6 nexthop flush
Dump was interrupted and may be inconsistent.
Flushed 2097152 nexthops

real	1m45.345s
user	0m0.001s
sys	0m0.005s

$ time sudo ip -6 nexthop flush
Dump was interrupted and may be inconsistent.
Flushed 4194304 nexthops

real	3m10.430s
user	0m0.002s
sys	0m0.004s

AFTER:
======

$ time sudo ip -6 nexthop flush
Dump was interrupted and may be inconsistent.
Flushed 2097152 nexthops

real	0m17.545s
user	0m0.003s
sys	0m0.003s

$ time sudo ip -6 nexthop flush
Dump was interrupted and may be inconsistent.
Flushed 4194304 nexthops

real	0m35.823s
user	0m0.002s
sys	0m0.004s

Signed-off-by: Christoph Paasch <cpaasch@openai.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250816-nexthop_dump-v2-2-491da3462118@openai.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-12-07 06:09:19 +09:00
arch powerpc/eeh: Use result of error_detected() in uevent 2025-12-07 06:09:19 +09:00
block blk-crypto: fix missing blktrace bio split events 2025-10-29 14:03:07 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:21:43 +02:00
Documentation Revert "docs/process/howto: Replace C89 with C11" 2025-12-07 06:09:15 +09:00
drivers char: misc: Does not request module for miscdevice with dynamic minor 2025-12-07 06:09:19 +09:00
fs NFSD: Fix crash in nfsd4_read_release() 2025-12-07 06:09:13 +09:00
include bpf: Don't use %pK through printk 2025-12-07 06:09:16 +09:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: fix possible deadlock in io_register_iowq_max_workers() 2024-11-17 15:06:25 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel uprobe: Do not emulate/sstep original instruction when ip is changed 2025-12-07 06:09:17 +09:00
lib minmax: don't use max() in situations that want a C constant expression 2025-10-19 16:21:52 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm minmax: make generic MIN() and MAX() macros available everywhere 2025-10-19 16:21:52 +02:00
net net: When removing nexthops, don't call synchronize_net if it is not necessary 2025-12-07 06:09:19 +09:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts locking: Introduce __cleanup() based infrastructure 2025-10-19 16:21:51 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:21:45 +02:00
sound ALSA: usb-audio: fix control pipe direction 2025-12-07 06:09:13 +09:00
tools selftests/net: Ensure assert() triggers in psock_tpacket.c 2025-12-07 06:09:18 +09:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-10-22 15:40:41 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS trace: Relocate event helper files 2024-04-10 16:19:24 +02:00
Makefile Linux 5.15.196 2025-10-29 14:03:16 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.