suspending execution within Xen

suspending execution within Xen

[Avi Kivity]

I am trying to send a stream of events about one domain to another. so I
set up a ring between the monitoring domain and xen (not the monitored
domain). however I am having trouble blocking when buffer space runs
out.

the intuitive

   while (!buffer_space_available())
       do_block();

does not work; do_block() appears to return to guest context, not to the
while loop (is this correct?). the other alternative,

    while (!buffer_space_available())
	if (!test_and_set_bit(EDF_BLOCKED, &ed->ed_flags))
	    domain_sleep(ed);

freezes xen solid.

is there a way to do it? am I missing something obvious?

Avi

Re: suspending execution within Xen

[Timenkov Yuri]

may be worth using wait queues here? (or schedule())

On Wednesday 29 June 2005 15:53, Avi Kivity wrote:
> I am trying to send a stream of events about one domain to another. so I
> set up a ring between the monitoring domain and xen (not the monitored
> domain). however I am having trouble blocking when buffer space runs
> out.
>
> the intuitive
>
>    while (!buffer_space_available())
>        do_block();
>
> does not work; do_block() appears to return to guest context, not to the
> while loop (is this correct?). the other alternative,
>
>     while (!buffer_space_available())
> 	if (!test_and_set_bit(EDF_BLOCKED, &ed->ed_flags))
> 	    domain_sleep(ed);
>
> freezes xen solid.
>
> is there a way to do it? am I missing something obvious?
>
> Avi
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

 -- 
Timenkov Yuri

Re: suspending execution within Xen

[Keir Fraser]

Xen on x86 doesn't support stack-based continuations within the 
hypervisor -- that is, there is no way to deschedule the current domain 
within Xen and then automatically return to your current point of 
execution when you are re-scheduled.

If you have further work to do, before returning to guest context, when 
the domain is rescheduled then you need to install your own hook 
function into vcpu->arch.schedule_tail. You'll need to xmalloc any 
space you need for continuation data.

  -- Keir

On 29 Jun 2005, at 12:53, Avi Kivity wrote:

> I am trying to send a stream of events about one domain to another. so 
> I
> set up a ring between the monitoring domain and xen (not the monitored
> domain). however I am having trouble blocking when buffer space runs
> out.
>
> the intuitive
>
>    while (!buffer_space_available())
>        do_block();
>
> does not work; do_block() appears to return to guest context, not to 
> the
> while loop (is this correct?). the other alternative,
>
>     while (!buffer_space_available())
> 	if (!test_and_set_bit(EDF_BLOCKED, &ed->ed_flags))
> 	    domain_sleep(ed);
>
> freezes xen solid.
>
> is there a way to do it? am I missing something obvious?
>
> Avi
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

Re: suspending execution within Xen

[Keir Fraser]

On 29 Jun 2005, at 13:03, Timenkov Yuri wrote:

> may be worth using wait queues here? (or schedule())

Xen's not Linux: the above primitives/functions do not exist.

  -- Keir

Re: suspending execution within Xen

[Avi Kivity]

On Wed, 2005-06-29 at 13:42 +0100, Keir Fraser wrote:
> Xen on x86 doesn't support stack-based continuations within the 
> hypervisor -- that is, there is no way to deschedule the current domain 
> within Xen and then automatically return to your current point of 
> execution when you are re-scheduled.
> 
> If you have further work to do, before returning to guest context, when 
> the domain is rescheduled then you need to install your own hook 
> function into vcpu->arch.schedule_tail. You'll need to xmalloc any 
> space you need for continuation data.
> 

this will probably serve. thanks.


>   -- Keir
> 
> On 29 Jun 2005, at 12:53, Avi Kivity wrote:
> 
> > I am trying to send a stream of events about one domain to another. so 
> > I
> > set up a ring between the monitoring domain and xen (not the monitored
> > domain). however I am having trouble blocking when buffer space runs
> > out.
> >
> > the intuitive
> >
> >    while (!buffer_space_available())
> >        do_block();
> >
> > does not work; do_block() appears to return to guest context, not to 
> > the
> > while loop (is this correct?). the other alternative,
> >
> >     while (!buffer_space_available())
> > 	if (!test_and_set_bit(EDF_BLOCKED, &ed->ed_flags))
> > 	    domain_sleep(ed);
> >
> > freezes xen solid.
> >
> > is there a way to do it? am I missing something obvious?
> >
> > Avi
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
>