Re: [Qemu-devel] [PATCH] tests/postcopy: Use KVM on ppc64 only if it is KVM-HV

[Thomas Huth]

On 16.11.2016 13:37, Greg Kurz wrote:
> On Wed, 16 Nov 2016 12:24:50 +0000
> "Dr. David Alan Gilbert" <address@hidden> wrote:
> 
>> * Greg Kurz (address@hidden) wrote:
>>> On Wed, 16 Nov 2016 09:39:31 +0100
>>> Thomas Huth <address@hidden> wrote:
>>>   
>>>> The ppc64 postcopy test does not work with KVM-PR, and it is also
>>>> causing annoying warning messages when run on a x86 host. So let's
>>>> use KVM here only if we know that we're running with KVM-HV (which
>>>> automatically also means that we're running on a ppc64 host), and
>>>> fall back to TCG otherwise.
>>>>   
>>>
>>> This patch addresses two issues actually:
>>> - the annoying warning when running on a ppc64 guest on a non-ppc64 host
>>> - the fact that KVM-PR seems to be currently broken
>>>
>>> I agree that the former makes sense, but what about the case of running
>>> a x86 guest on a non-x86 host ?

Of course you also get these '"kvm" accelerator not found' messages
there. But so far, I think nobody complained about that yet (only for
ppc64 running on x86). And at least the test succeeds there - unlike
with KVM-PR, where the test fails completely.

>>> I'm still feeling uncomfortable with the KVM-PR case... is this a workaround
>>> we want to keep until we find out what's going on or are we starting to
>>> partially deprecate KVM PR ? In any case, I guess we should document this
>>> and probably print some meaningful error message.  
>>
>> This is certainly a work around for now, it doesn't suggest anything about
>> deprecation.
> 
> Well it doesn't suggest anything actually, it just silently skips KVM PR...
> I would at least expect a comment in the code mentioning this is a
> workaround and maybe an explicit warning for the user. If the user really
> wants to run this test with KVM on ppc64, then she should ensure it is
> KVM HV.

Honestly, also considering the number of patches that Laurent already
wrote here and never have been accepted, all this has become quite an
ugly bike-shed painting discussion.

My opinion:

- If we want to properly test KVM (be it KVM-HV or KVM-PR), write
  a proper kvm-unit-test instead. I.e. I personally don't care if this
  test in QEMU is only run with TCG or with KVM.

- The current status of "make check" is broken, since it does not
  work on KVM-PR. We've got to fix that before the release.

That means I currently really don't care if we've spill out a warning
message for KVM-PR here or not - sure, somebody just got to look at
KVM-PR later, but that's IMHO off-topic for the test here in the QEMU
context.

So if you think that the patch for fixing this issue here with the QEMU
test should look differently, please propose a different patch instead.
I'm fine with every other approach as long as we get this fixed in time
for QEMU 2.8.

 Thomas