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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jun 28, 2018 at 09:27:08AM +0200, Dario Faggioli wrote:
> 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).

The shim uses CPU hotplug/unplug when the guest brings up/down a
vCPU using the VCPUOP_{up/down} hypercall.

The best description of the issue I could find is:

https://lists.xenproject.org/archives/html/xen-devel/2018-01/msg01085.html

Thanks, Roger.

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