Re: [Xen-devel] Clock Interrupt not occurring. hypervisor_callback not being called. (more info)

[Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>]

I can't explain why the atomic instructions wouldn't be sufficient.
I just thought it was worth a try to be explicit.
You should be able to create them with 'mb();'

-Dave



Ivan Kelly wrote:

> how would one create a memory barrier? I think the xchg asm
> instruction should be a natural barrier in any case.
> -Ivan
>
> On 3/1/06, Dave Winchell <dwinchell@xxxxxxxxxxxxxxx> wrote:
>  
>
> > Ivan,
> >
> > How about a memory barrier right before the call to evtchn_notify
> > in evtchn_set_pending and one before l1 =
> > x86_atomic_xchg(&s->evtchn_pending_sel, 0)
> > in do_hypervisor_callback?
> >
> > Regards,
> > Dave
> >
> >
> > Ivan Kelly wrote:
> >
> >    
> >
> > > Some more info on this problem.
> > > The problem seems to be that evtchn_pending[0] is not being updated
> > > fast enough after the callback is made. Therefore the callback is
> > > running and seeing nothing as pending and discarding anything that
> > > happens.
> > > If i put in something that delays before the start of the inner loop
> > > somewhere, it will work fine. It doesn't have to be a printf, can be a
> > > for(i=0;i<100000;i++) or something similar.
> > > evtchn_pending is set as volatile. Im not sure if this is actually
> > > helping at all though, since I have to use the ACK compiler which is
> > > the only thing that minix will compile with.
> > >
> > > Does anyone have any idea on how i can get evtchn_pending to update on time?
> > > Regards
> > > Ivan
> > >
> > >
> > >
> > >      
> > >
> > > > <SNIP>
> > > > PUBLIC void
> > > > do_hypervisor_callback(struct stackframe_s *regs)
> > > > {
> > > >       unsigned long  l1, l2;
> > > >       unsigned int   l1i, l2i, port;
> > > >       int            irq;
> > > >       shared_info_t *s = hypervisor_shared_info;
> > > >
> > > >       s->vcpu_data[0].evtchn_upcall_pending = 0;
> > > >
> > > >       l1 = x86_atomic_xchg(&s->evtchn_pending_sel, 0);
> > > >
> > > >       while ( l1 != 0 )
> > > >       {
> > > > /*              kprintf("l1: %x\n");*/
> > > >               l1i = x86_scan_forward(l1);
> > > >               l1 &= ~(1 << l1i);
> > > >
> > > >               l2 = s->evtchn_pending[l1i] & ~s->evtchn_mask[l1i];
> > > >               while ( l2 != 0 )
> > > >               {
> > > >                       kprintf("l2: %x\n", l2);
> > > >                       l2i = x86_scan_forward(l2);
> > > >                       l2 &= ~(1 << l2i);
> > > >
> > > >                       port = (l1i << 5) + l2i;
> > > >
> > > >                       if ( (irq = event_to_action[port]) != -1 ) {
> > > >                               do_event(irq, regs);
> > > >                       }
> > > >               }
> > > >       }
> > > > }
> > > > <ENDSNIP>
> > > >
> > > >
> > > >
> > > >        
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> > >
> > >
> > >      
> >    

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