Re: [Qemu-devel] [PATCH for-3.1] tests/cpu-plug-test: check CPU hotplug on ppc64 with KVM

[Thomas Huth]

On 07/27/2018 09:54 AM, Greg Kurz wrote:
> On Fri, 27 Jul 2018 15:27:24 +1000
> David Gibson <address@hidden> wrote:
> 
>> On Wed, Jul 25, 2018 at 04:45:26PM +0200, Greg Kurz wrote:
>>> Commit b585395b655 fixed a regression introduced by some recent changes
>>> in the XICS code, that was causing QEMU to crash instantly during CPU
>>> hotplug with KVM. This is typically the kind of bug we'd like our
>>> test suite to detect before it gets merged. Unfortunately, the current
>>> tests run with '-machine accel=qtest' and don't exercise KVM specific
>>> paths in QEMU.
>>>
>>> This patch hence changes add_pseries_test_case() to launch QEMU with
>>> '-machine accel=kvm' if KVM is available.
>>>
>>> A notable consequence is that the guest will execute SLOF, but for some
>>> reasons SLOF sometimes hits a program exception. This causes the guest
>>> to loop forever and the test to be stuck.  Since we don't need the guest
>>> to be truely running, let's pass -S to QEMU to avoid that.
>>>
>>> Also disable machine capabilities that could be unavailable in KVM, eg,
>>> when using PR KVM.
>>>
>>> Signed-off-by: Greg Kurz <address@hidden>  
>>
>> I'm pretty sure trying to change the accelerator on a qtest test just
>> doesn't make sense.  We'd need a different approach for testing cpu
>> hotplug against kvm & tcg backends.
>>
> 
> The test starts QEMU, triggers the CPU hotplug code with a QMP command
> and checks the command didn't fail (or QEMU didn't crash, as it would
> have before commit b585395b655a)... I really don't understand what
> is wrong with that... Please elaborate.

For a "real" test, I think you'd need a guest OS that is reacting to the
hot plug events. So maybe this should rather be done in the avocado
framework instead?

 Thomas