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Re: [Xen-devel] [PATCH v6 11/13] xen: support the Null scheduler

On Thu, 2018-06-14 at 13:20 -0700, Stefano Stabellini wrote:
> On Thu, 14 Jun 2018, Andrew Cooper wrote:
> > On 14/06/18 14:40, Jan Beulich wrote:
> > I don't think its reasonable to alter the support status with this
> issue
> > outstanding.
> I completely missed this report, probably because I haven't paid
> attention to PV-shim. Do you have any more information about this?
> The
> report is a bit vague. If I can't repro it, I can't fix it.
> Couldn't it be that is normal because after a while you ran out of
> pcpus?
> Dario, do you have any opinion on this?
The issue that I know of is that the null scheduler does not properly
support CPU hotplug/hotunplug.

This is an issue on, let's say, baremetal, if you use null, and try to
do CPU hotplug/hotunplug. When trying to use null as the scheduler of
the shim, we run into that same issue, even if not specifically doing
CPU hotplug/hotunplug (because the shim use the same path for CPU
bringup, IIRC).

In fact, I'm Cc-ing Roger as he's the one that found out the issue, and
we've discussed already a plan to fix it (that was mostly on IRC, so I
don't have a link, sorry).

FWIW, I am a little bit pressed with something right now, but fixing
this is very high in my todo list.

I think we should definitely aim at having null as supported for 4.12,
but I wouldn't mark it as such with known outstanding bugs.

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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