Xen devel - Feb 2006 - Clock Interrupt not occurring. hypervisor_callback not being called.

Im having a strange problem with a hypervisor_callback that I have written.
Im setting up VIRQ_TIMER and have added a handler for it. The evtchn_mask
bit, evtchn_pending bit, evtchn_upcall_mask, evtchn_upcall_pending and
evtchn_pending_sel>>5 bit are all zeroed.
I have a loop running, outputting text to the console in the main thread of
execution. When I run my kernel, this thread will run continuous, and never
be interrupted by the evtchn handler. Im printing out the values of all the
relevant fields(masks and pending etc) and they all seem to be set
correctly, but nothing happens.
Curiously, when I add a print statement to the do_hypervisor_callback
function, the callback seems to work correctly. Does anyone have any idea
why this could be happening?
Best regards
Ivan Kelly


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Have you tried making evtchn_pending and evtchn_mask volatile in
shared_info_t?

-Dave Winchell

Ivan Kelly wrote:
> Im having a strange problem with a hypervisor_callback that I have 
> written.
> Im setting up VIRQ_TIMER and have added a handler for it. The 
> evtchn_mask bit, evtchn_pending bit, evtchn_upcall_mask, 
> evtchn_upcall_pending and evtchn_pending_sel>>5 bit are all zeroed.
> I have a loop running, outputting text to the console in the main 
> thread of execution. When I run my kernel, this thread will run 
> continuous, and never be interrupted by the evtchn handler. Im 
> printing out the values of all the relevant fields(masks and pending 
> etc) and they all seem to be set correctly, but nothing happens.
> Curiously, when I add a print statement to the do_hypervisor_callback 
> function, the callback seems to work correctly. Does anyone have any 
> idea why this could be happening?
> Best regards
> Ivan Kelly
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.xensource.com
>http://lists.xensource.com/xen-devel
>  
>

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On 2/28/06, Dave Winchell <dwinchell@virtualiron.com>
wrote:
> Have you tried making evtchn_pending and evtchn_mask volatile in
> shared_info_t?
I tried that. It''s still showing the same behaviour.  The function is
as below. When the kprintf("l1 ... bit is uncommented, the clock
events seem to get fired fine, and the the main loop also continues to
run. When removed, it doesn''t get called at all. It never gets as far
as do_event. kprintf is a function that calls hypervisor_console_io.
This is 2.0.7 btw.
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>

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