yield() in kernel CAN'T yield control for MOD_LOAD thread

[John Baldwin]

On Thursday 26 August 2004 02:36 am, yangshazhou at hotmail.com wrote:
> Now "tsleep(&ident,PRIBIO,NULL,1)" solved the problem. Maybe yield() can't
> do the job in kernel. And mi_switch() is not enough to.Thank you.On

yield() can just switch back to you immediately since you (the current thread) 
are still runnable.  Use a sleep, either via sleep/wakeup, or doing a tsleep 
with a timeout forces the current thread to not be runnable for a while 
giving the other thread time to run.  Note that your tsleep(..., 1) is still 
racey, you really need to use sleep/wakeup to truly close the race.

> Wednesday 25 August 2004 03:06 am, yangshazhou at hotmail.com wrote:
> > Hi all,
> >     This problem delay me for quite a long time.
> >     I've built two klds, I'd like to see the result one's running to the
> > other's. In one kld's MOD_LOAD subroutine, I make a long 'for' loop, in
> > which it DELAY(1000) and then call yield(curthread,NULL). When the module
> > was loaded by kldload, the system failed to response until the loop quit.
> > The loop seems like that:
> >  for(i=0;i<8000;i++){
> >     ......
> >   DELAY(1000);
> >   yield(curthread,NULL);
> >  }
> >
> >     My system is 5.2.1-release. Thanks.
>
> You could try having the first one wait on a condition variable that the
> second module's MOD_LOAD does a wakeup on.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org