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Christoph Paasch e3efebfee6 net: When removing nexthops, don't call synchronize_net if it is not necessary
[ Upstream commit b0ac6d3b56a2384db151696cfda2836a8a961b6d ]

When removing a nexthop, commit
90f33bffa382 ("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>
2025-12-03 12:45:10 +01:00
arch powerpc/eeh: Use result of error_detected() in uevent 2025-12-03 12:45:09 +01:00
block block: use int to store blk_stack_limits() return value 2025-10-29 13:59:46 +01:00
certs
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-29 13:59:52 +01:00
Documentation arm64: errata: Apply workarounds for Neoverse-V3AE 2025-10-29 14:00:00 +01:00
drivers char: misc: Does not request module for miscdevice with dynamic minor 2025-12-03 12:45:10 +01:00
fs btrfs: use smp_mb__after_atomic() when forcing COW in create_pending_snapshot() 2025-12-03 12:45:04 +01:00
include bpf: Don't use %pK through printk 2025-12-03 12:45:06 +01:00
init
ipc
kernel uprobe: Do not emulate/sstep original instruction when ip is changed 2025-12-03 12:45:08 +01:00
lib lib/genalloc: fix device leak in of_gen_pool_get() 2025-10-29 13:59:53 +01:00
LICENSES
mm mm: hugetlb: avoid soft lockup when mprotect to large memory area 2025-10-29 13:59:50 +01:00
net net: When removing nexthops, don't call synchronize_net if it is not necessary 2025-12-03 12:45:10 +01:00
samples
scripts randstruct: gcc-plugin: Fix attribute addition 2025-09-09 18:44:01 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-29 14:00:01 +01:00
sound ASoC: qdsp6: q6asm: do not sleep while atomic 2025-12-03 12:45:05 +01:00
tools selftests/net: Ensure assert() triggers in psock_tpacket.c 2025-12-03 12:45:09 +01:00
usr
virt
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COPYING
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Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.4.301 2025-10-29 14:00:02 +01:00
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