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Re: [Xen-devel] dom0less + sched=null => broken in staging

On Fri, 9 Aug 2019, Dario Faggioli wrote:
> On Wed, 2019-08-07 at 11:22 -0700, Stefano Stabellini wrote:
> > Hi Dario, George,
> > 
> > Dom0less with sched=null is broken on staging, it simply hangs soon
> > after Xen is finished loading things. My impression is that vcpus are
> > not actually started. I did a git bisection and it pointed to:
> > 
> > commit d545f1d6c2519a183ed631cfca7aff0baf29fde5 (refs/bisect/bad)
> > Author: Dario Faggioli <dfaggioli@xxxxxxxx>
> > Date:   Mon Aug 5 11:50:55 2019 +0100
> > 
> >     xen: sched: deal with vCPUs being or becoming online or offline
> >     
> > Any ideas?
> > 
> Ok, I've done some basic testing, and inspected the code again, and
> honestly I am not finding anything really suspicious.
> Of course, I'm not really testing dom0less, and I'm not sure I can
> easily do that.
> Can you help me with this, e.g., by providing some more info and, if
> possible, logs?

I am attaching the logs. Interestingly, I get a bunch of:

(XEN) *** LOADING DOMU cpus=1 memory=40000KB ***
(XEN) sched_null.c:458: Not inserting d2v0 (not online!)

Maybe we are missing a call to online the vcpus somewhere in

> E.g., you say boot stops after Xen loading. Is there a bootlog that we
> can see (ideally from a debug build, and with "loglvl=all
> guest_loglvl=all")?
> Does the system respond to debug-keys? If yes, the log after triggering
> the 'r' debug-key would be useful.

The system doesn't respond to debug keys. My guess is that it is too
early maybe.

> These patches are about vcpus going offline and online... does dom0less
> play with vcpu onffline/online in any way?
> I've put together a debug patch (attached), focusing on what the
> mentioned commit does, but it's nothing more than a shot in the dark,
> for now...

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