Higher load averages running mysql on 15 instead fo 14

I upgraded all our machines to 15.0-STABLE last week. Which works fine, 
but I have noticed a very curious thing where the load averages on our 
main database machine have doubled.

See graph here...

https://api.ticketswitch.com/shared/mysql-load-average-14-to-15.png


The only thing which has changed there is the operating system, and
the re-install of the packages to match. All the versions are
identical, config is identical, workload is identical.

The CPU usage hasn't changed, just the load averages. If I look on
that machine, which is really only running mysql, then the processes
in mysql are all in the state "Waiting for table metadata lock"

My hope is that FreeBSD 15 somehow calculates load averages
differently, and I simply never noticed 100 processes
waiting on locks before. But I also worry that maybe mysql does
its locking using some operating system primitive, which has changed,
and is causing this.

Any ideas anyone ?

-pete.

PS: am also going to change the application to avoid 100 parallel
processes hitting that table at once, now I have seen this, but the
question as to why its changed still remains.