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
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.
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.
Cheers,
--
Julien Grall
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