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[ Upstream commitdf6afe2f7c] 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:90f33bffa3("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>
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.