Re: EARLY_AP_STARTUP hangs during boot

On Fri, 29 Jul 2016 13:17:42 -0700
John Baldwin <jhb_at_freebsd.org> wrote:

> On Thursday, July 28, 2016 12:31:31 AM Gary Jennejohn wrote:
> > Well, now I know that ULE is a prerequiste for EARLY_AP_STARTUP!  I
> > wasn't aware of that.  I prefer BSD and that's the scheduler I did
> > the first tests with.
> > 
> > But with the ULE scheduler the system comes up all the way.
> > 
> > It would be nice if the BSD scheduler could also be modified to
> > work with EARLY_AP_STARTUP.  
> 
> I wasn't able to reproduce your hang with 4BSD, but I think I see a
> possible problem.  Try this:
> 
> diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
> index 7de56b6..d53331a 100644
> --- a/sys/kern/sched_4bsd.c
> +++ b/sys/kern/sched_4bsd.c
> _at__at_ -327,7 +327,6 _at__at_ maybe_preempt(struct thread *td)
>  	 *  - The current thread has a higher (numerically lower) or
>  	 *    equivalent priority.  Note that this prevents curthread from
>  	 *    trying to preempt to itself.
> -	 *  - It is too early in the boot for context switches (cold is set).
>  	 *  - The current thread has an inhibitor set or is in the process of
>  	 *    exiting.  In this case, the current thread is about to switch
>  	 *    out anyways, so there's no point in preempting.  If we did,
> _at__at_ -348,7 +347,7 _at__at_ maybe_preempt(struct thread *td)
>  			("maybe_preempt: trying to run inhibited thread"));
>  	pri = td->td_priority;
>  	cpri = ctd->td_priority;
> -	if (panicstr != NULL || pri >= cpri || cold /* || dumping */ ||
> +	if (panicstr != NULL || pri >= cpri /* || dumping */ ||
>  	    TD_IS_INHIBITED(ctd))
>  		return (0);
>  #ifndef FULL_PREEMPTION
> _at__at_ -1127,7 +1126,7 _at__at_ forward_wakeup(int cpunum)
>  	if ((!forward_wakeup_enabled) ||
>  	     (forward_wakeup_use_mask == 0 && forward_wakeup_use_loop == 0))
>  		return (0);
> -	if (!smp_started || cold || panicstr)
> +	if (!smp_started || panicstr)
>  		return (0);
>  
>  	forward_wakeups_requested++;
> 

Thanks, but with this patch the kernel hangs in exactly the same
place as before - after the HPET output.

Maybe I'm missing some kernel option which ULE works around, or
something like that.

-- 
Gary Jennejohn