tree f3227f02202afaee658cc97697cdfa279eaf6f65
parent a7536ef9e1b5b8b83bc854fab53024e8cf61a6c4
author Willy Tarreau <w@1wt.eu> 1665514222 +0000
committer Willy Tarreau <w@1wt.eu> 1665577145 +0200
encoding latin1

MEDIUM: stick-table: make stksess_kill_if_expired() avoid the exclusive lock

stream_store_counters() calls stksess_kill_if_expired() for each active
counter. And this one takes an exclusive lock on the table before
checking if it has any work to do (hint: it almost never has since it
only wants to delete expired entries). However a lock is still neeed for
now to protect the ref_cnt, but we can do it atomically under the read
lock.

Let's change the mechanism. Now what we do is to check out of the lock
if the entry is expired. If it is, we take the write lock, expire it,
and decrement the refcount. Otherwise we just decrement the refcount
under a read lock. With this change alone, the config based on 3
trackers without the previous patches saw a 2.6x improvement, but here
it doesn't yet change anything because some heavy contention remains
on the lookup part.