[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

Hi Stefano,

On 06/29/2018 07:38 PM, Stefano Stabellini wrote:
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

I completely missed this report, probably because I haven't paid
attention to PV-shim. Do you have any more information about this?
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

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:


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.
Well, Mirela paved the way to support CPU hotplug (should be merged soon). She is looking at suspend/resume which is IHMO an extension of hotplug case. So are you sure this could never happen on Arm?

Also, supporting the hypercall would basically be ~20 lines. So I don't feel it is right to mark NULL scheduler supported on Arm until that is fixed in a way or another.


Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.