netdev - [RFC] net/packet: fix visible delays due to RCU sync

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Message-Id: <20220313100033.343442-1-equinox@diac24.net>
Date:   Sun, 13 Mar 2022 11:00:31 +0100
From:   David Lamparter <equinox@...c24.net>
To:     netdev@...r.kernel.org
Subject: [RFC] net/packet: fix visible delays due to RCU sync

Hi all,

while working with test setups that include a few hundred network
interfaces (not that unrealistic...), I ran into wireshark/dumpcap being
oddly slow to start up and decided to investigate.  Turns out it's
accumulating RCU delays (15ms, twice for each interface) - thise quickly
sum up.

Since synchronize_net() already does an expedited sync if RTNL is held,
I went and added a synchronize_net_expedited() for cases like this where
we have some other reason to want expedited sync.

Hope this is acceptable,

-David