HEADSUP: Turn off cpu_idle_hlt on SMP for now on x86

[Stephan Uphoff]

On Tue, 2005-02-22 at 17:59, Kris Kennaway wrote:
> On Tue, Feb 22, 2005 at 04:20:27PM -0500, John Baldwin wrote:
> > On Friday 11 February 2005 11:48 am, John Baldwin wrote:
> > > Thus, my theory is that when the pinned thread was preempted and put back
> > > on the run queue, the scheduler didn't IPI the CPU it was pinned to to wake
> > > it up in case it was idle.  The IPI is only needed if the CPUs are halted,
> > > which is why I think turning the idle halt off might work as a workaround. 
> > > I don't know if ULE has this same issue, but I've cc'd Jeff and hopefully
> > > he can look into it.
> > 
> > Nevermind, I don't think cpu_idle_hlt will help (though it has seemed to help 
> > locally oddly enough).  Presumably the CPU that the preempted thread owning 
> > the vm page queues lock would have run the pinned thread before going idle.  
> > In this case, that means that the thread must be pinned to CPU 0 which is 
> > running a make process that is just spinning.  Unfortunately we currently 
> > don't have a good way of looking at the stack for an thread on another CPU.
> 
> I'm running into this with deadlocks I'm seeing on a quad-cpu RELENG_5
> sparc machine.
> 
> Unfortunately, I can't even dump because of yet more locking assertion
> failures in the dump path (CAM, elsewhere).
> 
> Kris

The attached patch (hopefully ;-) fixes a few scheduler problems with
both SMP and UP.

The patch also adds an IPI to PREEMPT threads on other CPUs for i386.

While I compiled every valid combination of SMP,PREEMPT,FULL_PREEMPT I
did not have time to test all combinations.
( This needs a lot more testing - but I ran out of time)

Please test and provide feedback. 

Thanks
Stephan

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