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

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 08/30/04

  • Next message: John Baldwin: "Re: make "quickworld"? (like in DragonFly)" 
    To: freebsd-hackers@FreeBSD.org
Date: Mon, 30 Aug 2004 15:06:08 -0400

    On Thursday 26 August 2004 02:36 am, yangshazhou@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@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org
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