Re: Hypervisor crash(!) on xl cpupool-numa-split

[Stephan Diestelhorst <stephan.diestelhorst@amd.com>]

On Wednesday 02 February 2011 16:14:25 Juergen Gross wrote:
> On 02/02/11 15:39, Stephan Diestelhorst wrote:
> > We have the following theory of what happens:
> > * some vcpus of a particular domain are currently in the process of
> >    being moved to the new pool
> 
> The only _vcpus_ to be moved between pools are the idle vcpus. And those
> never contribute to accounting in credit scheduler.
> 
> We are moving _pcpus_ only (well, moving a domain between pools actually
> moves vcpus as well, but then the domain is paused).

How do you ensure that the domain is paused and stays that way? Pausing
the domain was what I had in mind, too...

> > Despite the rant, it is amazing to see the ability to move running
> > things around through this remote continuation trick! In my (ancient)
> > balancer experiments I added hypervisor-threads just for side-
> > stepping this issue..
> 
> I think the easiest way to solve the problem would be to move the cpu to the
> new pool in a tasklet. This is possible now, because tasklets are always
> executed in the idle vcpus.

Yep. That was exactly what I build. At the time stuff like that did
not exist (2005).

> OTOH I'd like to understand what is wrong with my current approach...

Nothing, in fact I like it. In my rant I complained about the fact
that splitting the critical section accross this continuation looks
scary, basically causing some generic red lights to turn on :-) And
making reasoning about the correctness a little complicated, but that
may well be a local issue ;-)

Stephan

-- 
Stephan Diestelhorst, AMD Operating System Research Center
stephan.diestelhorst@amd.com
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