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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 28 Jun 2018, Roger Pau Monné wrote:
> 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

OK, thanks for the explanation. We don't support CPU hotplug on ARM, so
we could mark the NULL scheduler as supported on the ARM architecture
today? Once you implement CPU hotplug support in NULL, we could mark it
as supported on x86 too.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel