[Xen-ia64-devel] Re: No scheduling after domU launch

[Haavard Bjerke <havard.bjerke@xxxxxxx>]

Here's an update on this bug. The problem seems to be the

asm volatile ("cmpxchg4.acq %0=[%1],%2,ar.ccv":
                      "=r"(ia64_intri_res) : "r"(ptr), "r"(new) : "memory");

line in gcc_intrin.h:ia64_cmpxchg4_acq(). When I comment it out when launching 
domU, things are back to normal.

The call sequence leading up to this instruction is:
sched_bvt.c:bvt_wake()
softirq.h:cpu_raise_softirq()
bitops.h:test_and_set_bit()
intrinsics.h:cmpxchg_acq() 
gcc_intrin.h:ia64_cmpxchg()
gcc_intrin.h:ia64_cmpxchg4_acq()

Håvard

On Thu, May 19, 2005 at 07:32:54PM +0200, Haavard Bjerke wrote:
> I think I've found some leads to the most recent bug (dom0 freezes 
> immediately, as opposed to after a short while). The problem seems to be 
> somewhere within the cpu_raise_softirq() routine, which is called from 
> bvt_wake() in sched_bvt.c. By not calling that routine when launching domU, 
> I've managed to get control back to dom0 for a short while, after which it 
> freezes as before. I'll look more into it tomorrow.
> 
> Håvard
> 
> On Wed, May 18, 2005 at 08:32:20AM -0700, Magenheimer, Dan (HP Labs Fort 
> Collins) wrote:
> > Given the previous discussion around this (last month?), I suspect
> > that there is a bug somewhere that is overwriting some random
> > memory related to the scheduler.  As Mark W pointed out, your
> > previous workaround fixed a problem that should never happen.
> > And I don't think any recent changes in xeno-unstable-ia64 have
> > had anything to do with the scheduler, so I suspect the
> > "random memory" moved to a different random spot which
> > is causing your current problem.
> > 
> > This is just a theory... you are probably as familiar with this
> > part of the code as anybody on this list right now.  Try
> > adding some more printf's to see if any clues arise.
> > I'll try to take a look but probably not today, so reply
> > to this thread if you learn anything new or interesting.
> > 
> > Dan
> > 
> > > -----Original Message-----
> > > From: Haavard Bjerke [mailto:havard.bjerke@xxxxxxx] 
> > > Sent: Wednesday, May 18, 2005 9:23 AM
> > > To: Magenheimer, Dan (HP Labs Fort Collins)
> > > Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> > > Subject: No scheduling after domU launch
> > > 
> > > Since pulling the latest xeno-unstable-ia64 a few days ago, 
> > > scheduling seems to stop immediately after launching domU, 
> > > that is, domU continues to load, while dom0 stops because the 
> > > scheduler is never entered again. This looks like the same 
> > > problem as before, with dom0 freezing after domU launch; 
> > > only, now it seems to freeze earlier. Before, I was able to 
> > > run a hypercall right after launch. This is kind of critical, 
> > > since a user-space app running in dom0 is supposed to 
> > > establish a ctrl-channel right after launch, while domU is booting.
> > > 
> > > So I'm quite stuck and wondering why it stops scheduling, and 
> > > I could use some input. So far I've found out that 
> > > __enter_sceduler() is never called after domU launch, while 
> > > the routine that's supposed to call that routine, 
> > > ac_timer_softirq_action(), continues to be called. I think 
> > > the __enter_sceduler() routine should be in a heap, but I 
> > > don't understand why it would suddenly be removed from the heap..
> > > 
> > > Thanks,
> > > Håvard
> > > 

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