timeouts too long bug again...

[Luigi Rizzo]

In sep.2009 i noticed that usleep() select() and friends (including
the in-kernel callouts) would consistently take one tick longer
than they should, and committed a fix to sys/kern/kern_timeout.c
to HEAD and RELENG_8

http://svnweb.freebsd.org/base?view=revision&revision=197137
http://svnweb.freebsd.org/base?view=revision&revision=200510

Now it seems that the bug is there again, in some form:
on 9.0 (and someone reported this also no HEAD) the minimum sleep
interval is now 2 ticks. Callouts seem to be correct (at least,
dummynet delays are exact, and the sysctl
	net.inet.ip.dummynet.tick_adjustment: 2770
now does not grow at 500 HZ as it did in the past.

Any idea on what might have reintroduced the problem ?

(please spare us the story that usleep gives no guarantees
etc etc - we all know that, but FreeBSD is consistently 1 tick
above the minimum guaranteed interval)

cheers
luigi