Re: domains being migrated state message improvements

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 02/05/14 17:46, Stefan Parvu wrote:
>> So a human can take a look at a system and see if anything looks
>> obviously wrong.
> and in our case, it is indeed wrong, or ... confusing - Man page says
> what we should expect from the state field.

Which manpage?

>  But instead we see ------
> How one should interpret that ? Even interactively :) vanished, not
> available, what really happened there ?! 
>
> First of all this should be documented and explained somewhere.

It is.  That would be "not running and not blocked" which is a valid
state for a VM to be in.

The comment in Xen still appears accurate:

    /*
     * - domain is marked as blocked only if all its vcpus are blocked
     * - domain is marked as running if any of its vcpus is running
     */

Blocked gets set whenever a vcpu uses a SCHEDOP_block or SCHEDOP_poll
hypercall.  The former for blocking until any event arrives, the latter
when waiting for a specific event.  SCHEDOP_block is used by guests when
idle.

With vcpu oversubscription, it is easy to have none of the vcpus running
at the moments when their state are sampled.  It is also easy for a
completely idle guest to have all vcpus blocked.

As a result, all 4 possible states of blocked/not blocked/running/not
running are valid.

Not blocked and not running therefore means "domain is not idle, but not
scheduled" which completely matches your description of oversubscribed
host with busy VMs.


>
>
>> How? it uses ncurses to be interactive on the terminal.  Collecting this
>> output with automated tools is impractical.
> you put xentop on batch mode to record data for long periods of time. 
> store it and analyze it. 

Wow - you learn something every day.  I was completely unaware of xentop
batch mode.

~Andrew