performance of jailed processes

[Dag-ErlingSmørgrav]

Can anyone explain why jailed processes seem to perform much worse
than non-jailed processes in recent -CURRENT?

Specifically, running a query against a remote MySQL server from
inside a jail takes an order of magnitude more time than from outside
the jail.  Tcpdump shows that the TCP packets carrying the result are
evenly spaced, so this is not a matter of the server timing out on a
DNS lookup or anything like that.

Running a configure script also takes much longer inside the jail than
outisde, and again, progress is even (though slow), so it is clearly
not a matter of DNS timing out.

There is no NFS or NIS in the equation either.  Parts of the file
space inside the jail is a nullfs mount, but we've also tried without
nullfs.

The system currently uses SCHED_ULE, but we had similar trouble with
SCHED_4BSD on 5.1-RELEASE before we went -CURRENT.

The machine currently has ~2600 processes running in ~400 jails.  Is
it conceivable that be scalability issues, perhaps in the credentials
code, could cause vastly increased syscall overhead for jailed
processes?

DES
-- 
Dag-Erling Smørgrav - des at des.no