is the hypervisor another domain?

is the hypervisor another domain?

[Diwaker Gupta]

Hi everyone,

I was just investigating scheduling of VMs on Xen, and so I was
logging the following data from inside __enter_scheduler (in
xen/common/schedule.c):

id: prev->id
duration: now - prev->lastschd

Now, suppose I have domain0 and another VM (the first created after
dom0, thus gets a domain ID of 1) running. And to simplify matters I'm
using the round robin scheduler with default params (i.e. 10ms slice).
Now I would have expected to see dom0 (id=0) and the lone VM (id=1)
scheduled alternately.

However, I see a lot of instances where the id as recorded above
reports a value of 32767. I'm guessing this is the hypervisor? It'll
be great if someone can shed some light on this -- does the scheduler
treat the hypervisor as just another domain?

It'll be great if someone can shed more light on whats going on here.

Thanks,
Diwaker
-- 
Diwaker Gupta
http://resolute.ucsd.edu/diwaker


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click

Re: is the hypervisor another domain?

[Rob Gardner]

Diwaker Gupta wrote:
> However, I see a lot of instances where the id as recorded above
> reports a value of 32767. I'm guessing this is the hypervisor? It'll
> be great if someone can shed some light on this -- does the scheduler
> treat the hypervisor as just another domain?

ID 32767 is the "idle" domain, which runs whenever there's no runnable 
domain.

Rob



-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click

Re: is the hypervisor another domain?

[Keir Fraser]

On 8 Mar 2005, at 20:13, Rob Gardner wrote:

> Diwaker Gupta wrote:
>> However, I see a lot of instances where the id as recorded above
>> reports a value of 32767. I'm guessing this is the hypervisor? It'll
>> be great if someone can shed some light on this -- does the scheduler
>> treat the hypervisor as just another domain?
>
> ID 32767 is the "idle" domain, which runs whenever there's no runnable 
> domain.

I think the round-robin scheduler might include the idle domain in the 
round-robin schedule. It really is very brain-dead -- I expect we will 
remove it as part of our current scheduler cleanups.

  -- Keir



-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click

Re: is the hypervisor another domain?

[Mark Williamson]

> I think the round-robin scheduler might include the idle domain in the
> round-robin schedule. It really is very brain-dead -- I expect we will
> remove it as part of our current scheduler cleanups.

Yes, it schedules everything on the runqueue, including the idle domain - it's 
only there as an example of the scheduler API.

It used to print "Stupid Round Robin Scheduler" at boot time but I think that 
got edited out ;-)

Cheers,
Mark


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click