luigi@hplabs.UUCP (Luigi Semenzato) (07/28/83)
I was looking at the 4.1BSD "scheduler" (sched(), in vmsched.c),
and I found out that it spends most of the time sleeping on
either of two events: "lbolt" or "runout", depending whether
"wantin" is set or not. The only place in which wantin is set is
in setrun() (or the equivalent part of wakeup()): if the process
to be run is not in memory, wantin is set. Also, if the
scheduler was sleeping on runout ("nothing to do, wake me up when
you need me") setrun() performs a wakeup() on runout.
It seems like the other sleep in sched() is of the type "I know
there is a process that wants to be brought in, but it doesn't
have enought priority right now, so I'll sleep for a while and
try again". Well, the problem is: every time sched() goes to
sleep, when it wakes up the first thing it does is clearing
wantin. Why does it do that? Does it EVER go to sleep on
lbolt? If yes, how? I am confused.
--
Luigi Semenzato HP Labs Palo Alto, CA 94304