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

From: Thomas Huth
Subject: Re: [Qemu-ppc] [PATCH] tests/postcopy: Use KVM on ppc64 only if it is KVM-HV
Date: Wed, 16 Nov 2016 14:17:47 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

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

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

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.


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