From: Ido Schimmel idosch@nvidia.com
[ Upstream commit df6afe2f7c19349de2ee560dc62ea4d9ad3ff889 ]
While insertion of 16k nexthops all using the same netdev ('dummy10') takes less than a second, deletion takes about 130 seconds:
# time -p ip -b nexthop.batch real 0.29 user 0.01 sys 0.15
# time -p ip link set dev dummy10 down real 131.03 user 0.06 sys 0.52
This is because of repeated calls to synchronize_rcu() whenever a nexthop is removed from a nexthop group:
# /usr/share/bcc/tools/offcputime -p `pgrep -nx ip` -K ... b'finish_task_switch' b'schedule' b'schedule_timeout' b'wait_for_completion' b'__wait_rcu_gp' b'synchronize_rcu.part.0' b'synchronize_rcu' b'__remove_nexthop' b'remove_nexthop' b'nexthop_flush_dev' b'nh_netdev_event' b'raw_notifier_call_chain' b'call_netdevice_notifiers_info' b'__dev_notify_flags' b'dev_change_flags' b'do_setlink' b'__rtnl_newlink' b'rtnl_newlink' b'rtnetlink_rcv_msg' b'netlink_rcv_skb' b'rtnetlink_rcv' b'netlink_unicast' b'netlink_sendmsg' b'____sys_sendmsg' b'___sys_sendmsg' b'__sys_sendmsg' b'__x64_sys_sendmsg' b'do_syscall_64' b'entry_SYSCALL_64_after_hwframe' - ip (277) 126554955
Since nexthops are always deleted under RTNL, synchronize_net() can be used instead. It will call synchronize_rcu_expedited() which only blocks for several microseconds as opposed to multiple milliseconds like synchronize_rcu().
With this patch deletion of 16k nexthops takes less than a second:
# time -p ip link set dev dummy10 down real 0.12 user 0.00 sys 0.04
Tested with fib_nexthops.sh which includes torture tests that prompted the initial change:
# ./fib_nexthops.sh ... Tests passed: 134 Tests failed: 0
Fixes: 90f33bffa382 ("nexthops: don't modify published nexthop groups") Signed-off-by: Ido Schimmel idosch@nvidia.com Reviewed-by: Jesse Brandeburg jesse.brandeburg@intel.com Reviewed-by: David Ahern dsahern@gmail.com Acked-by: Nikolay Aleksandrov nikolay@nvidia.com Link: https://lore.kernel.org/r/20201016172914.643282-1-idosch@idosch.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/nexthop.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -842,7 +842,7 @@ static void remove_nexthop_from_groups(s remove_nh_grp_entry(net, nhge, nlinfo);
/* make sure all see the newly published array before releasing rtnl */ - synchronize_rcu(); + synchronize_net(); }
static void remove_nexthop_group(struct nexthop *nh, struct nl_info *nlinfo)